  Cheat sensitive quantum bit commitment (CSQBC) loosens the security
requirement of quantum bit commitment (QBC), so that the existing impossibility
proofs of unconditionally secure QBC can be evaded. But here we analyze the
common features in all existing CSQBC protocols, and show that in any CSQBC
having these features, the receiver can always learn a non-trivial amount of
information on the sender's committed bit before it is unveiled, while his
cheating can pass the security check with a probability not less than 50%. The
sender's cheating is also studied. The optimal CSQBC protocols that can
minimize the sum of the cheating probabilities of both parties are found to be
trivial, as they are practically useless. We also discuss the possibility of
building a fair protocol in which both parties can cheat with equal
probabilities.
