[jQuery] Re: jQuery Effects (show, hide, slideUp, slideDown...) glitch with padding or margin

[Ambient.Impact]

That's because jQuery doesn't animate the padding and margin, you have
to do that yourself. You can see a similar issue on the jquery.com
main page, with the little demo. It jumps right at the start, when it
first becomes visible, probably because of margins. I don't know why
it would only occur at the end of the slideDown animation, though.