Simon / Doug,
We confirmed with the compliance team, and this is a special case for the AP3715i. There were some limitations observed during certification testing. So for these reasons when AN-HT40 is selected only the channels in the pull down shown below would be available. Channels 132/136 are permanently disabled for band edge issues and channels 116-120 and 124-128 are disabled for DFS Channel availability check reasons. Channel 140 is not allowed as it would only be bonded up to channel 144 which is not allowed. As a result, for the AP3715i you are limited to the existing channels shown in the pull down. Regards,
Dennis