The results of this bug varies: The map can be erased, or be replaced by another map.
1) Get 2 maps, a piece of paper, and a cartography table. The first map is Map#0.
2) Place the second map in the cartography table with a piece of paper
3) Pull out the new map with left-click, and place it back in the cartography table (it appears as Map#0 if you hover over it)
4) Either exit the table or shift-click the map, or pickup the map to put it back in your inventory.
5) Map#0 may be erased or take on the appearance of the second map.
Map#0 shows a blank map before exiting cartographer's table/removing map from active slot and putting it back.