diff --git a/VisualPinball.Engine.PinMAME.Test/PinMameGameDefinitionConverterTests.cs b/VisualPinball.Engine.PinMAME.Test/PinMameGameDefinitionConverterTests.cs
index 4f92f57..e2f3367 100644
--- a/VisualPinball.Engine.PinMAME.Test/PinMameGameDefinitionConverterTests.cs
+++ b/VisualPinball.Engine.PinMAME.Test/PinMameGameDefinitionConverterTests.cs
@@ -233,8 +233,9 @@ public void UsesPinMameNumberingForGenericFlipperSwitches()
 			Assert.That(definition.Diagnostics.Count(diagnostic => diagnostic.Contains("PinMAME's numbering")), Is.EqualTo(4));
 		}
 
-		[Test]
-		public void PrefersGenericFlipperButtonsOverMatrixCopies()
+		[TestCase(false)]
+		[TestCase(true)]
+		public void PrefersGenericFlipperButtonsOverMatrixCopies(bool conflictingMatrixButton)
 		{
 			// pre-Fliptronic WPC lists the matrix flipper switches as buttons too, like the published Bride of Pinbot
 			const string json = @"{
@@ -254,16 +255,46 @@ public void PrefersGenericFlipperButtonsOverMatrixCopies()
 				]
 			}";
 
-			var definition = PinMameGameDefinitionConverter.Convert(json);
+			var root = JObject.Parse(json);
+			if (conflictingMatrixButton) {
+				((JArray)root["inputs"]).Add(JObject.Parse(@"{ 'id': 'switch.matrix-13', 'label': 'Another Right Flipper Button', 'binding': { 'group': 'pinmame.input.switch', 'device': 13 }, 'roles': ['flipper.lower.right.button'] }"));
+			}
+			var definition = PinMameGameDefinitionConverter.Convert(root.ToString());
 
 			Assert.That(definition.Switches.Single(@switch => @switch.Id == "112").InputActionHint, Is.EqualTo(InputConstants.ActionRightFlipper));
 			Assert.That(definition.Switches.Single(@switch => @switch.Id == "114").InputActionHint, Is.EqualTo(InputConstants.ActionLeftFlipper));
 			Assert.That(definition.Switches.Single(@switch => @switch.Id == "11").InputActionHint, Is.Empty);
 			Assert.That(definition.Switches.Single(@switch => @switch.Id == "12").InputActionHint, Is.Empty);
+			Assert.That(definition.Diagnostics.Count(diagnostic => diagnostic.Contains("Duplicate input action")), Is.EqualTo(conflictingMatrixButton ? 2 : 0));
+			if (conflictingMatrixButton) {
+				Assert.That(definition.Switches.Single(@switch => @switch.Id == "13").InputActionHint, Is.Empty);
+			}
 			Assert.That(definition.Wires.Select(wire => $"{wire.SourceId}->{wire.DestinationId}"), Is.EquivalentTo(new[] { "112->46", "114->48" }));
 			Assert.That(definition.Diagnostics, Has.None.Contains("not imported"));
 		}
 
+		[Test]
+		public void ReportsDuplicateCabinetInputActions()
+		{
+			const string json = @"{
+				'format': 'pinmame-machine-definition',
+				'schema_version': 2,
+				'machine': { 'id': 'test.duplicate-start.2026', 'name': 'Duplicate Start' },
+				'coverage': { 'status': 'partial', 'completion_score': 50 },
+				'inputs': [
+					{ 'id': 'switch.start-1', 'label': 'Start', 'binding': { 'group': 'pinmame.input.switch', 'device': 1 }, 'roles': ['cabinet.start'] },
+					{ 'id': 'switch.start-2', 'label': 'Other Start', 'binding': { 'group': 'pinmame.input.switch', 'device': 2 }, 'roles': ['cabinet.start'] }
+				]
+			}";
+
+			var definition = PinMameGameDefinitionConverter.Convert(json);
+
+			Assert.That(definition.Switches.Single(@switch => @switch.Id == "1").InputActionHint, Is.EqualTo(InputConstants.ActionStartGame));
+			Assert.That(definition.Switches.Single(@switch => @switch.Id == "2").InputActionHint, Is.Empty);
+			Assert.That(definition.Switches.Single(@switch => @switch.Id == "2").InputMapHint, Is.Empty);
+			Assert.That(definition.Diagnostics, Has.Exactly(1).Contains("Duplicate input action"));
+		}
+
 		[Test]
 		public void DefaultsToTheParentRomListedAfterItsClones()
 		{
diff --git a/VisualPinball.Engine.PinMAME.Unity/Editor/PinMameGameDefinitionConverter.cs b/VisualPinball.Engine.PinMAME.Unity/Editor/PinMameGameDefinitionConverter.cs
index 7e8a81d..8551aca 100644
--- a/VisualPinball.Engine.PinMAME.Unity/Editor/PinMameGameDefinitionConverter.cs
+++ b/VisualPinball.Engine.PinMAME.Unity/Editor/PinMameGameDefinitionConverter.cs
@@ -249,12 +249,20 @@ private static List<GamelogicEngineSwitch> ConvertSwitches(JArray inputs, IReadO
 				.Where(@switch => !string.IsNullOrEmpty(@switch.InputActionHint))
 				.OrderBy(@switch => coreFlipperButtonIds.Contains(@switch.Id) ? 0 : 1)
 				.ToArray();
+			// One generic button plus one matrix copy is expected. Multiple candidates for the
+			// same action are ambiguous and must still produce mapping diagnostics.
+			var flipperMirrorIds = new HashSet<string>(actionClaimOrder
+				.GroupBy(@switch => @switch.InputActionHint, StringComparer.Ordinal)
+				.Where(group => group.Count() == 2 && group.Count(@switch => coreFlipperButtonIds.Contains(@switch.Id)) == 1)
+				.Select(group => group.Single(@switch => !coreFlipperButtonIds.Contains(@switch.Id)).Id), StringComparer.Ordinal);
 			foreach (var @switch in actionClaimOrder) {
 				if (inputActions.Add(@switch.InputActionHint)) {
 					continue;
 				}
 
-				diagnostics.Add($"Duplicate input action {@switch.InputActionHint}; switch {@switch.Id} ({@switch.Description}) was left available for manual mapping.");
+				if (!flipperMirrorIds.Contains(@switch.Id)) {
+					diagnostics.Add($"Duplicate input action {@switch.InputActionHint}; switch {@switch.Id} ({@switch.Description}) was left available for manual mapping.");
+				}
 				@switch.InputActionHint = string.Empty;
 				@switch.InputMapHint = string.Empty;
 			}