foomatic-3.0.2 depends on =net-print/foomatic-filters-3.0.2 but the latest stable version in portage of the filters is foomatic-filters-3.0.2-r1. (notice the -r1) I causes emerge -uD world to constanly upgrate to foomatic-filters-3.0.2-r1 and then downgrade to foomatic-filters-3.0.2.
aargh, we should always use ~ in depends instead of = thanks, fixed.