I was using a special-case text scrubber to cause this odd scenario, so it was my bug. But I assumed StylusStudio would help identify the error faster, and it didn't.
Subject:Is this really well-formed? Author:Neal Walters Date:11 May 2010 08:50 PM
Ok, maybe this could be a feature request then. I believe it's something a software tool should definitely, instead of relying on "eyeballs". Maybe you could have a WC3 Validate, and a Super-Strong Validate.