Yeah but it's not the client sending the resumption ticket but sending the capability in the ClientHello which exposes the session key under a possibly fixed key. So you can't fix this by busting the client cache I think. You need the capability flag off.

Even so could an active adversary turn on the capability in the ClientHello and still get a chance to see the STEK encrypted session key even against legacy (or intentionally ticket-disabled) clients? This I don't know - would a client just drop the ticket message and proceed or would it abort? But at least it would have to be an active attacker.