I have created maps, made copies and placed them on the walls in my house to mark my home on the map in my hand. I explored a little and when I found a village, I created a copy of the map for that area and put it on the wall in the village to act as a marker on the map I was carrying. This worked fine the first time. A little later I found another village in the same covered area of the map. created another copy and placed it on the wall. The marker from the first village dissapeared as well as the marker for my location. Now, each time I close the world and reopen it, all my markers will appear as well as my location for a short period and then quit working again. Going into the Nether creates two location markers for myself on the map as seen in the pictures included.