Only one Green Map marker appears in cloned maps

Every time I find a village, I like to clone my map and place it in an item frame to mark it with those helpful green markers. However, if I do this with more than one village on a map, either the new marker won't show up or the previous marker will disappear. I don't know if this is a bug or intentional, but it would be nice to have more than one green marker at a time on the maps.