The problem was diagnosed by Ken Thomases.

Currently drivers use DllMain(DLL_THREAD_DETACH) to release thread data.
The problem is that DLLs (like native urlmon.dll, esp. reproducible in
IE8) may still do user32 calls after driver detaches thread. Loader
ensures that since user32.dll was loaded before dependent DLLs, user32's
DllMain will be called in the right moment. Due to lazy loading of
drivers, we have no control over them. We may use a new entry point to
make sure that we detach user32 and driver at the same time.
Signed-off-by: Jacek Caban <jacek@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>