.42 seems to reintroduce a bug from V3.x that was fixed in .41: After powering up, the first DTMF key press you do gets "stretched" beyond when you release the key. It's not as bad as it was in V3x though (about a half second instead of two seconds).
Actually, the V4 code for N80 was available in late July/early August via Phoenix and the Nokia Service Centres... It just has been recently made available to the public via the new Nokia Updater App.