Fatal trap 30: reserved (unknown) fault

Hi.

About month ago after one of my amd64 8-CURRENT upgrade I have started 
to see crashes with very strange message:
Fatal trap 30: reserved (unknown) fault while in kernel mode

Crash usually happens during some driver loading or unloading, for 
example, snd_hda, which always worked fine before, or during ata channel 
detach/attach which also causes device destruction/creation. Backtrace 
of this state shows nothing interesting, for example idling in 
acpi_cpu_c1() or just DELAY().

Does anybody knows, for whom is this fault "reserved" and what does it mean?

-- 
Alexander Motin