suspend broken when disconnecting an usb audio device

[account lost]

Sorry about the mailing list chaos I'm creating, I hadn't subscribed and can't yet recover the message id to correctly reply to my previous message.

I reproduced the problem again in order to transcribe the accurate error message I'm getting, and noticed that this happens by simply plugging the usb sound card, even without setting it as the default hw.snd.default_unit and without opening any sound application at all.

In this case, instead of reading about which PID is still using the device, I get an error regarding the in kernel oss mixer 

PCM5: Waiting for sound application to exit!
PCM5: unregister: mixer busy