k9copy depends on only kde 4.1, so with USE=kdeprefix it keeps around the old kde 4.1 dir, kdelibs, kdepimlibs and others. Compiles and works (as far as i tested now) with kde 4.2 too.
Hm, i was not aware of this bug, but anyway i fixed in the tree. 2.1.0-r1 should work as expected.