1.next → 1.5.1
undecided → high
new → open
Thanks for taking the time to contribute to the jQuery project by writing a bug report and providing a test case!
You already resolved this ticket all by yourself with the comment. The part of the documentation you quoted applies directly to this ticket. As
backgroundPosition isn't a property with a single numeric value.
So this is basically a dupe of #7755 . You might want to look at my response there for a possible solution.
The reason I keep this ticket open is that this looks like a strange regression from 1.4.4 to 1.5, as there weren't that many changes to the css/animate related code afaik. So we should check what caused this to make sure we didn't break something else which IS supported.