Created attachment 16025 [details]
Test program to paint a pattern created in a group.
Painting with a pattern created by push_group/pop_group_to_source doesn't work. The attached program should fill the entire surface with red, but the generated pdf is white. Using the image or ps backends the bug doesn't appear.
This is the bug that test/group-paint exercises (except I choose blue and not red ;-)
That test also uses the default OVER operator (although for an opaque source I think the pdf backend treats OVER and SOURCE identically).