I'm updating the reason to one that fits a bit better since it does indeed seem you were right.
The new problem is youtube.php is acting as a proxy/content scraper and is going to their site and scraping all the links for videos matching a search. I've seen some youtube video sites here that don't get suspended because what they're embedding isn't questionable, AND because they have to manually enter the links. This one's using our bandwidth any time someone loads youtube.php because it goes to them to run the search, which uses up our bandwidth, and then comes back with the results.
Under the script hosting policy in our TOS which explicitly disallows content scraping, we can't do much with this one either way.