Comment 25 for bug 446373

The BadMatch error is returned from the render extension somewhere in this code block:

http://cgit.freedesktop.org/xorg/xserver/tree/render/picture.c?id=b2015a2c01711646bb7ae23d684abee0cd55d4d0#n1096

One reason would be that the mask pixmap is from another screen (no idea) or has the wrong depth (unlikely):

http://cgit.freedesktop.org/xorg/xserver/tree/render/picture.c?id=b2015a2c01711646bb7ae23d684abee0cd55d4d0#n1136

The other possibility is that *ps->ChangePictureClip() generates the BadMatch, but I have no idea where that call goes:

http://cgit.freedesktop.org/xorg/xserver/tree/render/picture.c?id=b2015a2c01711646bb7ae23d684abee0cd55d4d0#n1148