http://bugs.winehq.org/show_bug.cgi?id=24569
--- Comment #7 from Dmitry Timoshkov dmitry@codeweavers.com 2010-09-30 11:50:18 CDT --- Once again: Wine doesn't write anything to ~/.xsession-errors, all Wine output is printed to stderr.
You need to find out who redirects Wine output to ~/.xsession-errors, and file a bug report to its developers.
Regarding WINEDEBUG usage refer to the user documentation, or ask on the user support forum.