Hi guys!
I just installed Mint with Cinamon, and I have a little annoyance with it.
When some pop-up message window should disappear, a big grey blank window gets stuck on the top of the screen. (see screenshot)
It is "only" visible, that is I can click "through" it, but it is very annoying.
What could cause it, and how to get rid of it?
Thanks for your help!
Screenshot:



