And just to add: it is called "conflation" artifact and this is what AntiGrain Geometry used the compound shapescompound shapes rasterizer for, see:
flash_rasterizer.png http://agg.sourceforge.net/antigrain.com/demo/flash_rasterizer.png
(source: sourceforge.net)
Also, this is what NV Path Rendering claims to improve on:
An Introduction to NV_path_renderingAn Introduction to NV_path_rendering (p. 67) or NV_path_rendering FAQNV_path_rendering FAQ (#29).