Taskbar opens when I move my mouse down and left/right click.

Whenever I quickly move my mouse down whilst holding left or right click, say when im raze satcheling or placing a turret it will often make it so I open up my taskbar, it doesn't matter if its hidden or not, and reveal my cursor. If I was holding down left click at the time, my crosshair would be locked and if holding a gun, spamming. Basically, it's the equivalent of alt tabbing.