Why is jQuery UI accordion open/close animation so choppy?

css, html, javascript, jquery, jquery-ui

Solution

.ui-accordion .ui-accordion-content {
    padding: 1em 2.2em;
}

The issue is with this css. If you change it to px instead of em, it functions correctly.

Problem

I've been trying to figure this one out and I just can't see any issues - as well, the same accordion (same jqueryui version 1.9.2) works with no issues on another site, I even switched the theme to use the same one as the other site and I still get the choppiness on this one. And it shouldn't be the jquery ui theme either as it's working fine here Any ideas what it might be?

Original source