empty string on get css transform on first attempt

Hi,
I tried to get a div current transform using $('#mydiv').css('transform') and I get an empty string, but I know that this div has a transform: rotate(-1deg) css style applied via class reference.

If I set a rotation via $('#mydiv').css('transform', 'rotation(-1deg)') I can now read that value via the getter.
Any ideas?

I test on Mac Lion - Safari 5.1.5
