style bg_pixmaps and gtk_widget_shape_combine_mask

[Paul Barton-Davis <pbd Op Net>]

Any ideas on how I can use the pixmaps created by/for a style as a
mask in gtk_widget_shape_combine_mask() without getting a BadMatch
error from the Xserver ? 

I suspect its caused by the fact that the window for the widget
doesn't match the NULL window used to create the pixmap.

Ideas would be welcome.

--p