This paper addresses a problem that may damage the reliability of an interbank offered rate (IBOR) system. Using evidence from the Shanghai Interbank Offered Rate (SHIBOR), we show that some SHIBOR panel banks imitate peers’ quotes after observing them on the next business day. The strength of the intertemporal behavior can be measured by a “Signed Active-minus-Stationary (SAmS)” index, which significantly predicts SHIBOR changes. Moreover, we find that the consequences of the imitation behavior are not fully perceived and understood by the market, and, as a result, SHIBOR-linked derivatives are mispriced. Our findings suggest that regulators of a poll-based interest rate benchmark should pay attention to the intertemporal imitation of submissions, in addition to bad faith collusion. The SAmS index can be utilized in the quality control of panel bank submissions.