I accidentally just touched a key - it must have been 'E' - with a file open and TSD just exited! No warning, just gone. I re-opened and found that the Hot-keys are active all the time. For example, 'O' and 'U' close the open file without warning, but leave that file's address displayed at bottom-left of the main window. Unfortunately there seems to be no way to get back to it without restarting. I think this is a major problem :o
Should be fixed in the next version, too.