I will try to explain the root cause for this bug, it may help to understand the situation...
Basically, a piezoelectric crystal provides a very stable (~30 ppm or parts per millions, not per cent!) filter for an oscillator in the Mhz range, on the AR9331, it is either a 25 MHz or 40 MHz crystal.
However, the WiFi RF requires much higher frequencies in the 2.4 GHz range but still very stable, and moreover, the ability to have not a single stable but variable frequencies in this band in order to cover the different available channels.
This is achieved through the use of an electronic circuit called a PLL (Phase-Locked Loop) that uses the lowest frequency crystal-based oscillator to "drive" the highest frequency oscillator: when the highest frequency oscillator is "late" compared to the stable lowest frequency one, its is boosted a little, if "early", it is slowed down a little, so the highest frequency oscillator is "phased-locked" with the lowest one.
Unfortunately in the AR9331, it looks like that, changing the RF PLL frequency affects the USB clock, which is also derived from the single 25 MHz crystal-based oscillator by (I hope!) a separate PLL to generate the 12 MHz required for the Full-Speed USB OHCI controller clock. For an unknown reason, it does not affect the 480 MHz clock required by the separate High-Speed USB EHCI controller, which usually handles over FS traffic down to the OHCI one...
Thus, the AR9331 has a problem when starting the RF oscillator or changing the WiFi channel, and what the patch basically does is to "hold" the USB PLL while doing these actions.
But it looks like there is still a case that is not handled correctly when a client is not associated to an AP and regularly sends WiFi "Probe Request" packets on the different available channels to get a list of available APs, causing the same problem on the USB.
IMHO, it is not a major problem though, since when not associated, you can't do much anyway, but it is nevertheless the same bug, we just have to find where to put the missing workaround macro!
So I think you are safe as long as you are either an AP or an associated client, please report if not.