http://bugs.winehq.org/show_bug.cgi?id=10902
--- Comment #3 from Adam Klobukowski atari@gabo.pl 2007-12-27 06:32:32 --- PulseAudio OSS emulation uses LD_PRELOAD to inject dynamic library, that makes OSS access go directly into PulseAudio, so you can have few apps using it at the same time. At this moment I'm listening to two instances of VLC (under Wine), and one instance of Mplayer (native) all at once.
PulseAudio can have bugs, but this seems to be something wine related and how steam launches games - maybe it is something with linker?