Weird IE9 bug

This last two weeks I have dealt with a weird bug in IE9.

• The problem appeared in a legacy web application.
• The issue reported by the user was a combo that didn’t drop down.
• The problem appeared in different pages, but only for some combination of values.
• The issue appeared after installing IE9 from IE7 in a Windows Vista.
• The user could reproduce the issue (for a certain combination of values).
• We (both devs and ops) couldn’t reproduce in a standard machine even tough at work final users deal with a very standard machine (machine setups are pretty standarized at work).
• When we finally were able to reproduce in a standard machine, it only failed the first time a user logged in (second time, or even IE close rendered the bug irreproducible).
• We finally were able to pinpoint the problem to a very large option (as in 400 characters).
• And now I’ve been able to reproduce it with a reduced version of the page even in my setup (Vista64+IE9). See the gist. Save to a file, launch it with IE9 and try to change the option. We trimmed down to 200 chars (I guess even 150 chars wouldn’t be viewable).

UPDATE (2012-09-30): Tested on IE10 in Windows8 and seems to work fine.