I acquired a pair of shiny AR9220 minipci NICs last week - Ubiquiti SR71-12 and SR71-15. They're supposed to be like AR9280 but on PCI, not PCIe. Unfortunately they didn't work under FreeBSD. After some sleuthing (read: guessing), I stumbled across an ath9k commit which reworked some workaround for some AR9220's, which include the Ubiquiti SR71 versions.
There's also a bus error when reading a random register which is only referenced in a debug statement. That's a whole other bug to try and deal with.
But now I've verified that with both the AR9280 and the AR9220, the FreeBSD code is definitely tickling the radio wrong. Only one of the two radio chains is even active for the most part, and that chain seems to go deaf quite often, resulting in a baseband hang and chip reset. It also explains why I was getting absolutely shocking 11n performance out of it in my 11n branch.