It seems that if a user is editing a page and takes ages, they get timed out and get hit with the login page. What happens next is that they get a Moodle error page (can't remember the error sorry - something missing though).
Is there no way that the form text could still be accepted? I am a bit unclear how the login works (in respect of knowing where you wanted to go), I may need to look into this myself.
I have also experienced this but, not in a consistent way.