Ugly UI Slide Window animation glitch on external monitor when visor slides down

The visor appears on the bottom of the external monitor*, and then slides down into the top of my macbook screen. Ideally, it shouldn't show anything on the external monitor, but just slide down from the top of my main macbook screen.
- \- Arrangement of your displays in OSX make a difference. This is a problem if you have your secondary display above your macbook screen, and move your mouse up to get to it. If it is aligned to the right, the bug is not visible.