I've had that a few times lately too, both with my Chrome and Firefox. The only solution I've found is to save the draft and close it, then open it again from drafts. Most of the time it did indeed go (the ones it usually happens to me on I'm also sending to a group, so I can check the online archives).
Actually, now that I think about it, I'm really only getting that when on Firefox, not Chrome... guess it's not limited to a single browser.
--
Lily Tomlin - "No matter how cynical you get, it is impossible to keep up."