The multipolygon processing makes heavy use of the java.awt.Area class. Calling List<Area> allAreas = .....; List<Area> toRemoveAreas = .....; allAreas.removeAll(toRemoveAreas); sometimes does not remove the areas in toRemoveAreas but some more. The patch does not longer use removeAll but checks for identity before removing an area. (I hope I found all places...) As a result sometimes some inner polygons were not cut out from the outer polygon. WanMil