Thanks Mark, it would seem that you are not alone in receiving very poor service from Yahoo! (perhaps that's why they've gone from being a world leader to pretty much a joke in the search world when compared to the likes of Google and Microsoft)
These errors seem to have been known since at least 2007 and their support haven't learned anything in 6 years -
www.webmaster-talk.com/html-forum/86887-...page.html#post392908
I knew that that was not our code but it took me longer than it should have to find how they were injecting it... i'm posting the screenshots here below so that others may benefit from this, at least until we have a Wiki...
The telling file is whv2_001.js which is not one of ours but is injected by their server to do tracking... or at least try to... apparently it breaks the layout (as well as the javascript) in more than a few websites...
Glad you got it sorted though... another triumph against the soothsayers...
John