Resolved! Is it normal to see negative channel cost values?
This is taken from an AP230 running 8.2r4: Lowest cost channel: 120, lowest-cost: -1280 Channel 36 Cost: -1280 Channel 40 Cost: 1309 Channel 44 Cost: 792 Channel 48 Cost: 1055 Channel 52 Cost: 796 Channel 56 Cost: 279 Channel 60 Cost: ...