Could reproduce it!
The steps to go:
1.) Create a FirstPerson example project in 4.8
2.) Convert it in place to 4.9
3.) Set up the PlayerController to receive mouse events using this tutorial: Mouse Control Setup | Unreal Engine Documentation
4.) Create a C++ based Actor and add mouse event handling (see ‘MyActor.cpp’ in ‘Source.7z’)
5.) Create a BP Actor based on C++ class MyActor.
6.) Change the AFirstPersonGameMode.cpp like in ‘Source.7z’, so that a BP Actor is spawned and mouse cursor is shown in StartPlay()
7.) Disable AFirstPersonCharacter::OnFire(), (see ’ AFirstPersonCharacter.cpp’ in ‘Source.7z’)
8.) Create a UserWidget BP. Add nothing to it. Canvas only in enough.
9.) Create BP from your AFirstPersonCharacter if not already there.
10.) In the BP of AFirstPersonCharacter at event StartPlay spawn the UserWidget BP, set it to viewport, and SetVisibility to hidden.
11.) Compile and Start simulation. There should be a box spawning near the player. If you hover the mouse over the box, the cursor should change. If you click on the box, it should disappear.
12.) Change the BP of AFirstPersonCharacter. set the visibility of the UserWidget to visible.
13.) Compile and start again. This time the box should not receive mouse events.