The XORG QXL driver uses a slower hash function than the Win32 one.
The hash in Xorg's QXL is done in qxl_image.c , hash_and_copy() function.
The hash in Win32's QXL is done in display/res.c , GetHash() function.
Fixed by commit http://cgit.freedesktop.org/xorg/driver/xf86-video-qxl/commit/?id=70d0d49b7c7d115f297dae710b9bb62b97fa22d5
That's because I pushed it an hour ago.