Pushing back a window pushes it "under the desktop" (it is still visible, but clicks on that window fail). Is that a known bug or a setting?

Question

I seem to have a weird one on one of my VirtualBox installation.

I installed Ubuntu 20.04 a while back (fresh, not an upgrade) and I have been running on there nicely for a while. Then I upgraded to 22.04. Since then I have a really weird error happening: when I push a window to the back (Lower function, I set it up on Alt-F6) then the window is unresponsive to mouse clicks. The two ways I can rescue that window is by using the Raise key (I set that to Alt-F7) twice or by clicking on the icon in the bar (but that's not practical when you have many editors open...)

I'm wondering whether I hit a bug in the Desktop or whether this is a setup issue that I could fix by tweaking a preference somewhere.

Note 1: I'm running with VirtualBox 6.1

Note 2: Restarting Gnome doesn't help (i.e. Non-focused windows not responding to mouse clicks)