vchans seem to affect /dev/dsp* availability

When I have vchans enabled, every few attempts at opening /dev/dsp* result in 
'Operation not supported by device.'  Also, while they're enabled, some 
programs (most reproduceably artsd) peg my CPU after outputting sound data in 
certain situations.

Disabling vchans fixes the problem.  The problem's a little ephemeral, so I'm 
still collecting hard data, but it seems I have to go all the way to properly 
disable them, e.g.
kldload snd_pcm
sysctl hw.snd.maxautovchans=0
kldload snd_<my card>

Simply turning them off after the drivers have been loaded does not seem 
sufficient.

I've been seeing this on my laptop since I -currentified it, which was early 
this month.  I dismissed it as CS4281-specific until it began happening on my 
desktop with a recent build, on both a VIA VT8235-style AC97 chip -and- my 
SBLive.

Thoughts?  I'm going to try reverting a few of the source files to see if it 
resolves itself, but pointers from those involved would be much appreciated.

Thanks!

-Cliff L. Biffle