http://bugs.winehq.org/show_bug.cgi?id=24569
--- Comment #8 from Jerome Leclanche adys.wh@gmail.com 2010-09-30 12:14:07 CDT --- (In reply to comment #7)
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.
IIUC, X automatically redirects stderr->xsession-errors if the program was not opened from a terminal.