In 'Coherence Mode', windows that I've sized & positioned a certain way are suddenly made smaller...

I typically use Parallels in Coherence Mode, and I have 2-3 windows sized and positioned a certain way on one of my Mac's desktop screens (swipe gesture to go to desktop or a mouse hotkey click). Sometimes, either over night when I return to my desk the next morning, or after a few hours during the day, when I return to view of these windows, the positioning has completely changed and the size has shrunk; and the 2-3 windows are just on top of one another in a corner. A tad annoying since I have to re-size and re-position them the way I want.

What might be causing this and how could I fix it?

Thank you