Do you mean a forum post reply? Using the Quick Reply feature? Could you post a screenshot?
Yes, Rob, it happens to the forum post reply window on IE but only when using the "Quote" button (or when quotes, images etc. are inserted manually). The reply button at the bottom of the page works OK but only if there are no quotes inserted in the reply. This glitch was present with the previous software as well. Firefox doesn't seem to have this problem at all as I recently found out, so it's probably an IE issue.
PS. Taking screenshots, I'm afraid, is out of my league, but I hope you got the idea.