I am curious about this too. After disabling javascript and fiddling with this for about 1.5 minutes in Web Inspector I was able to get it to behave like the JS implementation reasonably reliably. It would only have required some CSS cleanup to move the icons etc. back into place properly.
Ah, I see. The problem is that I'm an idiot and was :fixing the wrong div. For some reason it was collapsing ingloriously upon itself. Must've been a 3 AM hackjob.
Also, I'm gonna shrink the header for all of the content pages. Good call.