Select tag z-index glitch in IE

I thought this was fixed for IE7, but not so.

Set Up:
We have a page with 3 tabbed divs; only one is displayed at a time, while the others are display: none. The default div that displays on load contains a select tag which changes the content in a table inside that div based on date. The second div displays a dynamically generated table in standard HTML. The third and last div contains a Flash movie.


Problem:
In IE 6 & 7, when the second tab is clicked to hide the first div and display the second div, there is a mystery horizontal rule (at the same height as the top of the table in the first div). This line seems to be on the top layer, and causes anything below the line to be unclickable.


Solution:
Quickie: remove the <select> tag and use something else (custom slider or create the select menu as a DHTML drop-down instead).

This sounds like it could be fixed with the jQuery iframe method, but we haven’t tried it yet.

But what I want to know is why the select still creates the bug when it’s containing element has display: none. Does display: none mean that all the included elements are still lurking underneath? This makes no sense since normally, display: none causes the page to change size.