Yeah, not exactly sure what happened. The "TMC" style originates from some previous version of vBulletin.
Tracking down those sort of problems is supposed to be MPT's job and I alerted him via email some hours ago. In the mean time I made a new vanilla style that is at least native to vB4 and stuck our header on it.
So change the style to "TMC--vB4". Though it's not perfect, it's better actually in a lot of ways, so try it out.