I ran into a really weird bug this morning. I was having an issue with a jQuery plug-in I wrote, where for some reason IE7 was not triggering the onmouseover event properly. After spending a bunch of time trying to track down the problem, I finally realized that it wasn't triggering the event until it got inside the padding of the element—which is the wrong behavior.
I whipped up a quick test case of a <div> with onmouseevent and some padding, but that worked as expected (with the event firing as soon as it reached the padding of the element.) As I started to debug the problem, I added a background color to the root element in order to see if I could tell when the even actually fired. However, as soon as I added the background-color, the event started firing correctly.
I'm not exactly sure what combination of HTML/CSS is causing the problem. I've been trying to to put together a straightforward example that illustrates the problem, but I've yet to be able to recreate without really complex code.
I believe the problem is related to having an absolutely positioned parent element with relatively positioned children and then moving the parent item's position in the DOM. Even stranger was that if I hide the entire content and would re-show it, everything would work properly.
It sounds like it's a pretty obscure buried bug, but if you're ever having problems getting an event to fire properly in IE7, try defining a background-color for the element to see if that fixes the problem.