What did I do:
So I was setting up a display panel with circuit conditions, and pressed tab by accident.
What happened:
Game immediately switched to map mode, as that button is meant to do. Unfortunately it also closed the display panel modal, which meant I lost all the changes. No prompt, no nothing.
What I expected to happen:
Since modals closing is normal behaviour shared with everything else, I'd expect going to map mode would save the changes. This isn't an issue for other windows where there is no "are you sure you want to save changes" interaction. I can't really think of another object settings window that would request confirmation either way.
Either preserve the modal on the map window or save the changes.
Does it happen every time?
Yes.
[2.0.15] opening map while editing display panel settings closes the window without saving
Re: [2.0.15] opening map while editing display panel settings closes the window without saving
I've reported a similar issue a while back in 2.0.14: 119518. Opening the research window while editing a display panel also wipes the unsaved changes without confirmation, though it leaves the display panel GUI open. I've just tested it in 2.0.20 and the issue is still in the game.