Hah glad you found it. Yeah if you give the main content div any kind of transform3d property local coordinates are created and that interferes with this a bit. Which is what I'm doing.It was a serious question... I don't know what the question was?
I think you may want to prepend to </body>. It's of course only necessary to make this fix to support themes that do this to main content. We do it so the animation on collapsing the sidebar is smoother.