Game freezes when cursor is moved...

What the title says. I was doing a Posi TF last night, when I noticed this strange bug. Upon entering the mission, any movement of the cursor would freeze the game. At first I thought it was just a laggy mission, but it persisted throughout the whole mission. I could move and look around with the keyboard, but any movement of the mouse would freeze the game until you stopped.

This problem stayed even after the mission. I rebooted my computer, and that fixed the problem for the time being. Does anybody know what exactly was happening there?