The border of MS Office applications have their z-order set to the front. Even though the applications are in the background, the mouse thinks they are in the foreground and tries to resize. A visualization might help. The white <-> arrow is the captured mouse cursor.
Does anyone know how to fix this? I am using a licensed Crossover 20 (trying to use Support only as needed). Tested with Office 365 Powerpoint, Word, Excel. This does not happen on other Windows applications.
The impact is most dramatic when trying to use Linux software that you are often clicking in many different locations. But anything that you click on can cause a Windows app to suddenly jump to the front.