diff --git a/Assets/Tests/InputSystem/Unity.InputSystem.Tests.asmdef b/Assets/Tests/InputSystem/Unity.InputSystem.Tests.asmdef
index c855eb5ce6..7c7a31cd0a 100644
--- a/Assets/Tests/InputSystem/Unity.InputSystem.Tests.asmdef
+++ b/Assets/Tests/InputSystem/Unity.InputSystem.Tests.asmdef
@@ -72,6 +72,11 @@
             "expression": "6000.3.0a6",
             "define": "UNITY_INPUT_SYSTEM_PLATFORM_POLLING_FREQUENCY"
         },
+        {
+            "name": "Unity",
+            "expression": "6000.4.0a4",
+            "define": "UNITY_INPUTSYSTEM_SUPPORTS_MOUSE_SCRIPT_EVENTS"
+        },
         {
             "name": "Unity",
             "expression": "6000.5.0a8",
diff --git a/Packages/com.unity.inputsystem/CHANGELOG.md b/Packages/com.unity.inputsystem/CHANGELOG.md
index 3453304eb6..953e472618 100644
--- a/Packages/com.unity.inputsystem/CHANGELOG.md
+++ b/Packages/com.unity.inputsystem/CHANGELOG.md
@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed an incorrect ArraysHelper.HaveDuplicateReferences implementation that didn't use its arguments right [ISXB-1792] (https://github.com/Unity-Technologies/InputSystem/pull/2376)
 - Fixed `InputAction.IsPressed`, `WasPressedThisFrame`, and `WasReleasedThisFrame` using a `ButtonControl`'s `pressPoint` when a binding also had an explicit `PressInteraction` with its own `pressPoint`, which could make those APIs disagree with the interaction's press and release behavior. Action-level press APIs now follow the interaction threshold when both are set explicitly.
 - Fixed `IndexOutOfRangeException` in `InputDeviceBuilder` when connecting an HID gamepad whose report descriptor declares a hat switch with Report Size 8 (e.g. ESP32-BLE-Gamepad). The HID layer now anchors the hat's directional sub-controls to the hat's own byte instead of letting the layout system auto-allocate a fresh byte for each [UUM-143659](https://jira.unity3d.com/browse/UUM-143659).
+- Fixed `OnMouseUpAsButton` and `OnMouseUp` being dropped in Play mode when the Game view's focus changes between a press and its release on Unity 6000.5.0a8 and newer. The legacy `SendMouseEvents` pipeline is no longer driven from `InputUpdateType.Editor` updates, which read the editor state buffer (position (0,0), not pressed) and produced a spurious mouse release that cleared the press target.
 
 ### Changed
 - Action-level `IsPressed`, `WasPressedThisFrame`, and `WasReleasedThisFrame` for bindings to `Vector2Control` / `StickControl` no longer consult a per-control `pressPoint` on the vector (that field was removed). Use a `Press` interaction to set a custom threshold, or rely on `defaultButtonPressPoint`.
diff --git a/Packages/com.unity.inputsystem/InputSystem/Runtime/InputManager.cs b/Packages/com.unity.inputsystem/InputSystem/Runtime/InputManager.cs
index dc89828362..d396770da4 100644
--- a/Packages/com.unity.inputsystem/InputSystem/Runtime/InputManager.cs
+++ b/Packages/com.unity.inputsystem/InputSystem/Runtime/InputManager.cs
@@ -4069,7 +4069,9 @@ private void FinalizeUpdate(InputUpdateType updateType)
             //send pointer data to backend for OnMouseEvents
 #if UNITY_INPUTSYSTEM_SUPPORTS_MOUSE_SCRIPT_EVENTS
             var pointer = Pointer.current;
-            if (pointer != null && pointer.added && gameIsPlaying)
+            // Skip during InputUpdateType.Editor: pointer reads the editor state buffer (position (0,0), not pressed),
+            // which would emit a spurious release and drop OnMouseUp/OnMouseUpAsButton on the real release.
+            if (pointer != null && pointer.added && gameIsPlaying && updateType != InputUpdateType.Editor)
                 NativeInputSystem.DoSendMouseEvents(pointer.press.isPressed, pointer.press.wasPressedThisFrame, pointer.position.x.value, pointer.position.y.value);
 #endif
             m_CurrentUpdate = default;