Yeah, here's one that took a while to track down.
If you are able, check out this HTML in IE6:
This is a much-stripped-down segment of a web page I'm working on, generated by ASP.Net. It is generated by two standard ASP.Net validators (one Custom and one Required) set to Display="Dynamic" and a standard ASP.Net DropDownList inside a standard, run-of-the-mill HTML table cell, with an element from an included stylesheet thrown on. What you will see is a select box, with the last bunch of bytes from the list of options displayed below it. This text cannot be clicked or selected, the IE Developer Toolbar disavows any knowledge of its existence, and it's obviously not in the source as plain text. The text does appear in the select box where it's supposed to be; there's just a duplicate, unexplained copy on the screen. The amount of text displayed varies from select box to select box -- there is another that is in an AJAX UpdatePanel that loads a very long list of names that only displays the very last character from the very last option.
This appears just fine in IE7, Firefox, and Opera (and probably most others).
What I found, as I was systematically stripping styles and other elements off of the page, is this only seems to occur when there are two validators both with Display="Dynamic" (rendered as "display:none" in the span styles), and only in a table cell. Remove either validator or change its Display property to Static or None makes it go away.
Of course, removing validators or changing their display wasn't going to be the answer -- there are too many pages and too many different ways validators are drawn and used to alter. But as I was going through the stylesheet, I found this block of code:
I commented out the "float:left", and sure enough, the problem went away. You can try it yourself by either removing the "float:left" on the SELECT tag, or changing it to "float:none".
Why are we floating all input elements left? I'm about to find out, but considering just about everything is in a div or table cell, I'm guessing (and hoping) this style element can be removed safely...