I must be slipping -- took me the better part of 10 minutes to crash it!
I created a trivial document and clicked File | Save As ... I then clicked the up arrow button to move up one directory level, and then double clicked on another directory. Note that when the dialog first opens, the file name field has the focus, but after navigating around that's no longer true (although the cursor is still in it). I then hit a key and LyX crashed.
Clicking in the file name field before typing (after navigating to a new directory) works fine. Curiously, if I choose File | Save as, navigate to a new directory, change focus to a different program, change back to LyX and hit a key, LyX does not crash (but the key I typed does not go into the file name field, either). So methinks focus has something to do with it.
I've got some other items I'll post in separate headings (to keep the subject lines clear), unless someone tells me they'd rather get omnibus messages.
-- Paul