How to fix black screen on El Capitan (10.11.3)?

Hello all,

I don't know the proper terminology for things so apologies in advance. Basically, when I use the new El Capitan feature that lets you put windows side-by-side, and I do this with a flashcard program on one side and iBooks on the other, then I hit the "Close" button (not the upper-left red X but a button that says "Close" in the program) on the flashcard, the side the flashcard was on goes black. I then hit the green button in the upper-left of the iBooks window so that it pops back out. Unfortunately, I then try to do the three-finger swipe between full-screen programs and there is a black screen that shows up as a full-screen program. If I linger on this screen, it pauses for a brief moment before snapping back to the original screen (screen #1).

Does anyone know what I'm talking about? Can you help me get rid of the black full-screen? If I restart my computer everything is fine ... perhaps I should just stop hitting the "Close" button and using the red X in the upper-left for the flashcard program. Just wondering if anyone knows anything about this.

Thanks!