Animating background-position fails in IE8

[lgarvey]

I'm attempting to animate a background image. As per the following jsfiddle:

​http://jsfiddle.net/vEaMd/2/

This fails in IE8 ultimately because

 jQuery.css('backgroundPositionX')

on the div returns "right". In chrome it returns "100%" and in firefox it returns nothing. This breaks the animation since it cannot retrieve the starting position of the background to be animated.

The $.css inconsistency can be easily tested using the following jsfiddle:

​http://jsfiddle.net/Zqj7t/

If someone can point me towards a jQuery test that fixes a similar cross-browser inconsistency I'd gladly write up a proper test-case and submit a patch via github

[dmethvin]

Duplicate of #11971.