diff --git a/api/filters/patchstrategicmerge/patchstrategicmerge_test.go b/api/filters/patchstrategicmerge/patchstrategicmerge_test.go
index 867f83db6..6c69968c7 100644
--- a/api/filters/patchstrategicmerge/patchstrategicmerge_test.go
+++ b/api/filters/patchstrategicmerge/patchstrategicmerge_test.go
@@ -370,6 +370,212 @@ spec:
         image: test2
       - name: test
         image: test
+`,
+		},
+		// the following tests document broken behavior and
+		// will be fixed
+		// ref: #3111, #3159
+		"list map keys - add a port, no names": {
+			input: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+         protocol: TCP
+`,
+			patch: yaml.MustParse(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+         protocol: UDP
+       - containerPort: 80
+         protocol: UDP
+`),
+			expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+        - containerPort: 80
+          protocol: UDP
+`,
+		},
+		"list map keys - add name to port": {
+			input: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+         protocol: UDP
+       - containerPort: 8080
+         protocol: TCP
+`,
+			patch: yaml.MustParse(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+         protocol: UDP
+         name: UDP-name-patch
+`),
+			expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`,
+		},
+		"list map keys - replace port name": {
+			input: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+         protocol: UDP
+         name: UDP-name-original
+       - containerPort: 8080
+         protocol: TCP
+         name: TCP-name-original
+`,
+			patch: yaml.MustParse(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+         protocol: UDP
+         name: UDP-name-patch
+`),
+			expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+          name: TCP-name-original
+`,
+		},
+
+		// the following tests document behavior
+		// that should not be affected by
+		// changes due to #3111, #3159
+		"list map keys - add a port, no protocol": {
+			input: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 8080
+`,
+			patch: yaml.MustParse(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: test-deployment
+spec:
+ template:
+   spec:
+     containers:
+     - image: test-image
+       name: test-deployment
+       ports:
+       - containerPort: 80
+`),
+			expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 80
+        - containerPort: 8080
 `,
 		},
 	}
diff --git a/kyaml/yaml/merge3/element_test.go b/kyaml/yaml/merge3/element_test.go
index 9b685c1c8..ca1626f30 100644
--- a/kyaml/yaml/merge3/element_test.go
+++ b/kyaml/yaml/merge3/element_test.go
@@ -917,4 +917,621 @@ spec:
 `,
 		infer: false,
 	},
+
+	// The following test cases are regression tests
+	// that should not be broken as a result of
+	// #3111, #3159
+
+	//
+	// Test Case
+	//
+	{
+		description: `Add a containerPort to an existing list`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+        - containerPort: 80
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+        - containerPort: 80
+`},
+
+	//
+	// Test Case
+	//
+	{
+		description: `Add a containerPort to a non-existing list, existing in dest`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 80
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 80
+        - containerPort: 8080
+`},
+
+	//
+	// Test Case
+	//
+	{
+		description: `Add a name to containerPort`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          name: 8080-port-update
+        - containerPort: 80
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+        - containerPort: 80
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          name: 8080-port-update
+        - containerPort: 80
+`},
+	//
+	// Test Case
+	//
+	{
+		description: `Update protocol for a port`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`},
+	//
+	// Test Case
+	//
+	{
+		description: `Append container port`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 80
+          protocol: HTTP
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 80
+          protocol: HTTP
+        - protocol: TCP
+          containerPort: 8080
+`},
+
+	{
+		description: `Update container-port name`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+          name: foo
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+          name: bar
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+          name: foo
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+          name: bar
+`},
+
+	// The following test cases document broken behavior
+	// that will change as a result of #3111, #3159
+
+	//
+	// Test Case
+	//
+{
+	description: `Add a containerPort with protocol to an existing list`,
+	origin: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`,
+	update: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+        - containerPort: 8080
+          protocol: TCP
+`,
+	local: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`, // output should have both
+	expected: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`},
+
+//
+// Test Case
+//
+{
+description: `Add a containerPort with protocol to a non-existing list, existing in dest`,
+origin: `
+apiVersion: apps/v1
+kind: Deployment`,
+update: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`,
+local: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`, // output should have both
+expected: `
+apiVersion: apps/v1
+kind: Deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`},
+
+	//
+	// Test Case
+	//
+	{
+		description: `Merge with name for same container-port`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+          name: original
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+          name: original
+        - containerPort: 8080
+          protocol: TCP
+          name: updated
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+          name: original
+        - containerPort: 8080
+          protocol: HTTP
+          name: local
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+          name: original
+        - containerPort: 8080
+          protocol: UDP
+          name: original
+`},
+
+	{
+		description: `Retain local protocol`,
+		origin: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: UDP
+`,
+		update: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`,
+		local: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: HTTP
+`,
+		expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-deployment
+spec:
+  template:
+    spec:
+      containers:
+      - image: test-image
+        name: test-deployment
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+`},
 }