Attempt to switch to multi-window logs me out of my current session

Very recently installed Linux Mint 21, Mate Edition.
Installed Gimp 2.10.30.
Opened Gimp, unchecked Windows:Single-Window Mode
and was immediately logged out of my current user session.
Had to log back in.

I have been using Gimp on Ubuntu Mate 20.04 for a couple years
with no problems.

Has anyone heard of this problem or could offer help?

This is the GNOME project: if you have issues with Mint and/or MATE, I strongly encourage you to use their forums for support.