None. Mutts have fleas, not bugs.
Suspend/resume while editing a file with an external editor does not work under SunOS 4.x if you use the curses lib in /usr/5lib. It does work with the S-Lang library, however.
Resizing the screen while using an external pager causes Mutt to go haywire on some systems.
Suspend/resume does not work under Ultrix.
The help line for the index menu is not updated if you change the bindings for one of the functions listed while Mutt is running.
For a more up-to-date list of bugs, errm, fleas, please visit the mutt project's bug tracking system under http://bugs.mutt.org/.
Hmmm. Shouldn't http://bugs.mutt.org be http://fleas.mutt.org? If so, wouldn't that subdomain be a bug, er, I mean, flea? Maybe I should file that if not already...