Not sure what the previous nightly was that I would have been on, but it seems the crash only occurred after I added a new CD and rescanned. That is, it was running fine on that nightly, only when it went to update the database that it failed.
At a guess the only nightly I wouldn’t have updated to recently would be svn-1433 (ie I think I went from svn-1417 straight to svn-1441).
Stopping Firefly, deleting the songs.db and restarting caused the database+schema recreation and scanning of everything to work fine (and seemed quite a bit quicker than last time I did that on the NSLU2 too!), so not a big problem by any stretch of the imagination.