MRF24WB0M, on the product level, only supports legacy 802.11 data rates of 1Mbps and 2Mbps.
However when MRF24WB0M transmits an association request to an AP, MRF24WB0M will advertise in the supported rates information element (IE) rates of 1, 2, 5.5 and 11 Mbps.
This is not a bug and is intentional, leveraging from our past experiences.
If MRF24WB0M module just advertises 1,2 Mbps, most APs out in the field have a tendency to drop MRF24WB0M module and not permit connection to the MRF24WB0M module. Therefore for APs compatibility reasons, MRF24WB0M will advertise supported rates reflecting that of the APs. For example, the beacon from the AP will advertise supported rates of 1, 2, 5.5, 11, 18, 24, 36 and 54 Mbps. MRF24WB0M will duplicate the 802.11b rates in this information and advertise supported rates of 1, 2, 5.5 and 11 Mbps in the association request frame supported rates IE field.
However, the tradeoff is that APs, thinking that MRF24WB0M module supports 1,2,5.5, 11 Mbps, starts transmitting 11 Mbps and this will cause eventually wireless connectivity to fail as MRF24WB0M module will not be able to receive the AP's transmissions. However, bear in mind, according to 802.11 specifications, broadcast frames are to be transmitted at base rates of 1 and 2 Mbps. At the same time, this trend may start changing as the push for higher rates persist.
Bear in mind that MRF24WB0M module is meant for a captive environment, whereby the 802.11 network is known.