http://bugs.winehq.org/show_bug.cgi?id=26576
--- Comment #5 from Dan Kegel dank@kegel.com 2011-03-28 20:15:21 CDT --- It's case sensitive, you would need
WINEDEBUG=warn+heap wine Steam.exe -applaunch 48190 > log.txt 2>&1
We would also want the log from that if the error persisted.
You didn't say you were using PlayOnLinux, though. That invalidates your initial bug report, since you probably aren't using the version of wine you thought you were.
Please try again with vanilla wine-1.3.16, without playonlinux, just to be sure.