Just a small headsup, this happened to me twice before. Im not so sure that its a bug than its an oversight on the way the editor auto-arranges events, since popups arent linked to map objects and therefore can get switched freely between maps.
However, using undo (CTRL-Z) does work, assuming you dont exit or preview. Saved a dozen lines of text in one case for me.
It would be nice if we could 'fix' popups to a particular map.