Before that I wrote to the mailing list about the problem and this is what I got a reply.
But based on this patchwork it seems like they added a method of more
accurately detecting failure to change from a low power state. I guess
if it power state was being changed often sometimes their detection
wouldn't catch the failure... the wireless card may have just been
busy doing a scan or some other sort of operation and wasn't able to
respond to the power state change request quickly enough, and so
you're seeing a nagging warning.
UPD. nope. the error also appears randomly on the vanilla kernel
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