Comment # 21 on bug 900273 from Oliver Neukum

(In reply to Takashi Iwai from comment #20)
> Thanks for tracking down!
> 
> So, it comes from USB, but a specific device.  Oliver, any idea?

We might be hitting a race with the poll for medium change. Can you try with
the attribute "events_poll_msecs" for the device in sysfs set to -1?