Fully agree, it is odd.
I wonder what would happen if you disable the 802.11g data rates (6, 9, 12, 18, 24, 36, 48, and 54 Mbps) from the Mandatory rates in order to force 802.11n (if the scanner supports it)
Furthermore, do you think that there are 802.11b clients nearby? This would also trigger the protection mechanism (even if they are not connected to your network)
Kevin