For the past few days now, I've come across a peculiar error with my Dock. It won't respond to my mouse moving down to the bottom of the screen until I click it, and when it does, it won't change the active icon when I drag my mouse over it. Here's a video of what happens.
This is accompanied by a peculiar error in Mission Control where I can't click on windows to enter them until I drag them a little bit. Here's a video of that phenomenon.
Update: I've found out that this happens when I attach my external mouse (a Cyborg R.A.T. 5) to the computer. I'll test other external mice and then maybe file a bug report with Apple.