Yes, see below. What you see here, is a Transmission window (a Qt application) on top of a much larger Firefox window. In this window a small area (it is NOT a window) shows the actual content of the larger Transmission window. And the rest of this window is a copy of the covered underlying Firefox window or it is transparent(?).
As soon as I change the Transmission window size with a mouse drag, the small area completely fills the Transmission window. So then it is normal again.
I do not have a screenshot of a Calibre window. I rebooted my system and now can not reproduce this behaviour 
. Strange!
