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.