Extra markup added more than once

In the Embed filter settings page it says:
Markup that should appear directly before an <object>, <embed> or <script> tag. This only applies to the outermost tag in the case where nested tags are found.

However, it seems like the extra markup is added more than once for code containing nested tags. The code I've used for my the pre tag is:
<div class="video">
and the one for the post tag is:
</div>

The code for the video (directly copied from YouTube) is:
<object width="425" height="350"><param name="movie" value="http://www.youtube.com/v/vdQj2ohqCBk"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/vdQj2ohqCBk" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350"></embed></object>

However, when the page contaning the video is displayed, the following code is output:

As you can see the <div class="video"> snippet is added more than once... Any idea why that is and how to go about fixing it? Thanks in advance.