We show that claims of “perfect security” for keys produced by quantum key exchange (QKE) are limited to “privacy” and “integrity.” Unlike a one-time pad, QKE does not necessarily enable Sender and Receiver to pretend later to have established a different key. This result is puzzling in light of Mayers’ “No-Go” theorem showing the impossibility of quantum bit commitment. But even though a simple and intuitive application of Mayers’ protocol transformation appears sufficient to provide deniability (else QBC would be possible), we show several reasons why such conclusions are ill-founded. Mayers’ transformation arguments, while sound for QBC, are insufficient to establish deniability in QKE.