Originally reported by Boris Zbarsky on the list:
"The image surface that _cairo_quartz_surface_acquire_source_image creates never
seems to be released, probably because there is no release_source_image callback
in the quartz code.

The attached patch fixes that problem, at least insofar as the image surface
itself is no longer leaking.  I'm not sure whether any other cleanup needs to
happen here."

To reproduce, change test/source-pattern.c to #include "cairo-quartz.h", then replace the call to cairo_image_surface_create with a call to cairo_quartz_surface_create. Wrap all the code of the test in while(1) and monitor the memory of the process when you run the test.

Boris' patch is obviously correct, and applying it the leak disappears. Just recording the issue here for the benefit of the log, I'll close the bug in a moment or two.