I saw that briefly when I was testing, but I wasn't able to get it to repro again.
Without a repro, I am thinking it is a caching problem, or a loading sequence problem with tinyMCE.
Try reloading the page while holding down the ctrl key and see if it is still happening.
I am posting with IE8 right now, and it can work correctly.
But when editing, the initial display does not expand correctly. I am thinking that there is some sort of problem with the current release of tinyMCE. They have just made a major update and may not have all of the bugs worked out.