See 'Bugfixes' section of the TO-DO list for additional known bugs. There are a number of them there as well.
Strange things can happen.
Some users have seen intermittent problems with XEmacs version 19.13 not being refreshed correctly after a restart of fvwm2. If this occurs, you should be able to open a new frame and delete the old one. I can't debug this, as I don't see this problem. I don't know if the problem is from XEmacs, fvwm2, or something specific to a few user's setups. Some users have been getting odd startup problems, like total lockups.