I just checked and it isn’t the case for my blog. Check on an individual basis; perhaps it’s happening when the posts are made in IE. I had some stray code attached a few days ago, but have been posting in Firefox lately and no extra tags have been added.
At YouTube itself today, I noticed a few problems; random bits of code appearing on pages, etc. Double-check your own posts to make sure there’s no extraneous code and if it’s still a problem, drop YouTube a line. I’m going to check my blog out with IE6 in a few hours. My readers are complaining they can’t see anything with IE.