Previously hovered buttons in-game activate when clicking out of window and into the background of game

When you mouseover a button, then click somewhere else in the window, and the button activates even if your mouse isn't near said button.

HOW TO INITIATE:
1. open game (make sure it isn't in full-screen)
2. hover mouse over the play button.
3. click outside the game window (taskbar or another window).
4. click inside the game window, but on the panorama.

EXPECTED/ACTUAL:
nothing should happen when clicking anything other than a button or slider, but it does when these steps are followed.