Embedded video duplicated after editing

Something weird is going on with embedded video. When I paste in some embed code from Youtube, it works fine the first time.

But when I go back and edit that same message (don't make any changes) the video is duplicated - there are two of it.

The original "source" code looks like this:

<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/I4S2Gu7ZDT0&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/I4S2Gu7ZDT0&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>