Ui ignores mouse input in Unity Player, works in Standalone Build

Unity Version: 5.3.4f1

As title states, I start the game inside Unity with the play button and inside the game tab with the preview of the Game, no click or mouse Input is registered, the game seems to ignore them alltogether.

The same game, built with the Win_x86 build process works, all clicks and input is registered as intended.

I checked the scene hierarchy as the game was running in preview and checked if there are any gui elements overlaying or covering up clickable gui elements, but couldn't find anything that might be interefering.

Any idea on how to approach this problem?

// EDIT:

I figured out how to make it work again, but am not sure why I have to do this:

In the EventSystem in every Scene, I have "Standalone Input Module" Components. I have to manually go to the scene tab while running the game, go to the inspector and check "Force Module Active".

The Game doesn't seem to be able to detect the correct input method in the preview functionality.

Is there a way to fix this?