It's *supposed* to only trigger that message when there's an error that would cause the 'invalid markup, user must manually fix' message to print in an entry, but the HTML parser is a hornets nest so I'm not terribly surprised it's doing something slightly weird.

I'll go digging, but as a temporary workaround, you can switch off the beta 'create entry' page - the check only runs on that, not on the old one.