This paper investigates inter-piconet interference (IPI) in the multi-band orthogonal frequency division multi-plexing (MB-OFDM) ultra-wideband (UWB) standard. IPI is caused when the time-frequency codes (TFCs) that delineate MB-OFDM piconets collide. An upper-bound on the severity of the IPI problem is obtained through a theoretical analysis of data-rate-specific punctured convolutional codes. Using these results, several methods for adaptive TFCs are proposed and analyzed. Comprehensive simulation results show how packet error rates (PERs) for simultaneous operating piconets (SOPs) can be improved by up to 2 dB by enabling adaptive TFCs at the transmitter. Several combinations of data rate, TFC, channel model and interferer power are studied.