While playing on a LAN multiplayer with my wife, we had a map going, with 3 copies of said map.  one on a wall and each of us holding the others.  Things were normal until we tried out the new map markers function.  we set up our marker for home and suddenly our personal markers which are usually... white? ... don't remember.... turned black.  This was odd but we kept going.  when we later found a village, we attempted to mark that location with a white banner.  it too was all black on the map.  This began to make the map markers less functionally useful in all honesty.  I tried removing the banner and replacing it with different colors but no matter what, everything (except our first banner-marker) was all black.  rebooting did nothing to fix things either. We also removed the map from the item frame on the wall, no change.