Media Plugin Breaks Site

I'm running a number of sites and am using the TinyMCE editor on all of them... and am using the Media plug-in to facilitate the embedding of Flash videos (ie: YouTube, etc.) in blogs and other postings.

On one of the sites, for some reason the posting of a YouTube vid breaks the #main container and spits out everything at the bottom of the page.

When I look at the page source it shows...

<div class="node ntype-webfun" id="node-1156">
<div class="content">
<p><object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0" width="425" height="350"></p>
<param name="width" value="425" />
<param name="height" value="350" />
<param name="src" value="http://www.youtube.com/v/VXVdNKciP94" />
<embed type="application/x-shockwave-flash" width="425" height="350" src="http://www.youtube.com/v/VXVdNKciP94"></embed>
<br />
</object>
</p>
</div>
</div>

Yet, when I look at it with Firebug... it looks like this:

<div id="node-1156" class="node ntype-webfun">
<div class="content">
<p>
<object width="425" height="350" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0"/>
</p>
</div>
</div>
</div>
</div>
</div>
<param value="425" name="width"/>
<param value="350" name="height"/>
<param value="http://www.youtube.com/v/VXVdNKciP94" name="src"/>
<embed width="425" height="350" src="http://www.youtube.com/v/VXVdNKciP94" type="application/x-shockwave-flash"/>
<br/>

I've looked at the CSS, and there's nothing assigned to object in it...

I find if I remove the <object></object> tags, it embeds properly and doesn't break the container -- but that requires some manual HTML editing, and I don't want my content editors getting their hands messy.

Thoughts?