We address the problem of MAC-layer misbehavior in distributed multi-channel MAC protocols. We show that selfish users can manipulate the protocol parameters to gain an unfair share of the available bandwidth, while remaining undetected. We identify optimal misbehavior strategies that can lead to the isolation of a subset of frequency bands for exclusive use by the misbehaving nodes and evaluate their impact on performance and fairness. We develop corresponding detection and mitigation strategies that practically eliminate the misbehavior gains. To the best of our knowledge, this is the first attempt in characterizing the impact of misbehavior on multi-channel MAC protocols.