I have a lot of problems this time of year with false dfs events on pmp450. Running 126.96.36.199 firmware and when we have cool nights and warm days (south Texas) we see dfs detections all over on the network. One example out of many: I have an ap with 5620 primary, 5570 secondary, and 5480 tertiary frequencies and all morning long it gets dfs events on all three channels. Once the sun comes up a bit and it warms up it stops.
I am also here in south texas and have PMP 450 and 450i but have no problem but my radios are on 15.0.3 firmware. Have you tried to upgrade them? Perhaps that will do the job.
I have not. My medusa's are running 15.03, but not the 450 or 450i. I'll give that a shot! Thank you