Occasionally I reply to an email and it goes through the process, with the progress bar just like a successful email, but it doesn't show up in my sent box or my drafts - it just disappears. Is there a fix for this?

The only thing I can think is that I hit reply, then added a recipient to the cc. It's not the first time this has happened and I think I did the same thing the last time - added a recipient. Suggestions?