Black screen during change of spaces Using OS X 10.11.3, Mac Pro 5,1, 32GB RAM, Radeon HD 7950 (Sapphire) graphics card w/ 3GB VRAM. I have a multiple monitor setup with displays not having separate Spaces. Usually, when using a shortcut key to change spaces, I see a nice animation where one space slides to the left, and the new space slides in from the right.

However, once I have around six "desktops" and/or a certain number (unknown) of windows open, the animation displays a black screen when sliding the new space into place. Happens in both "directions" - the current space slides left/right, and the black screen slides in. Once the changing of the space is complete, the black goes away and the desktop reappears. This video shows the phenomena at 0:15s.

Anyone encounter this and find out why this might be occurring? Never happened with the same hardware using OS X versions prior to 10.10.
It is not a GPU issue.
With OS X 10.11, this can be corrected by turning Dashboard off or setting it as an overlay (System Preferences>Mission Control).