I've verified the issue on a test application. The developer mode is producing a warning message about that missing style. I've filed a bug to have this resolved. The good news is is that this warning message is only present in developer mode and not live. Your live applications should not be affected.
Good to know - I didn't realize that this was breaking the form submission process. The bug has been picked up and already repaired, and will go out in our next patch release of the platform slated for early in June.