You've accidentally set 'm' as a hotkey in the compose window, (one which 'apparently' dopes nothing). Check your settings, if you find it, remove the hotkey by hovering the cursor over that menu item and hit the 'delete' key. Then perhaps turn 'enable customisable keyboard shortcuts' off (Preferences/Miscellaneous).
with regards Paul -- It isn't worth a nickel to two guys like you or me, but to a collector it is worth a fortune -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org