Yes, it's awkward when that happens - and I've done it a few times.  I don't know of a quick way of escaping from it other than killing the program.

By mistake I pressed F12 (message properties) instead of the intended F11 (Set colours) when in a folder window when all messages in the folder had been selected.

Both the Cancel and Exit (X) buttons - and Escape key -  had exactly the same effect as pressing OK so several hundred mouse clicks were needed to escape from the pop-up.

Is this normal behaviour?

Bob