it is not just you; it happens to me, too. hitting back after submitting has become a habit for me, personally. i believe this is because the url it is refreshing to is not being handled properly, somehow. (which is odd, since it looks the same to me as one that works.)
relatedly, i would like to see the "talk" frame start acting more liek the chatterbox nodelet, meaning telling you what you msg'd to whom.
however, to nitpick, that isn't framechat. that's the PM frames interface to the chatterbox, which seems to be nameless. framechat is a client written by epoptai.