There is a "gutter" in between each pair of adjacent maps at the same zoom level within which the player marker is not displayed correctly. When the player's world coordinates correspond to a pixel in this gutter, his player marker has the dot shape on both adjacent maps. It should always have the pointer shape on one or the other.

The gutter occurs on every edge of every locator map and is 1 pixel wide. Since the number of blocks mapped by a pixel depends on the zoom level, this corresponds to a variable number of blocks in the mapped area: 1 block for Level 0 maps, 2 blocks for Level 1 maps, 4 blocks for Level 2 maps, 8 blocks for level 3 maps, and 16 blocks for level 4 maps. The actual number of blocks where the bug can be observed is actually twice this number, because each map has its own gutter and they are adjacent to each other. Thus, when using zoom level 4 maps there is a 32 block wide zone centered on every map boundary within which your player marker is displayed as a dot when it should be a pointer.

As a consequence of this bug, if you watch a map while you walk, waiting for the pointer to change to a dot, and immediately create a new map when it does, you will get a duplicate of the map you thought you just left. In addition, if you carry adjacent maps and try to switch to the next map when your pointer changes to a dot, you will find that your marker is a dot on both adjacent maps, which is confusing and disorienting. The effect gets worse with higher zoom levels because the gutters map more blocks in the world.

Steps to reproduce:
1. In Creative Mode, go to coordinates (0, 0) and use an Empty Locator Map to create a filled map. It should be named Map 1.
2. Go to coordinates (128, 0) and create another filled map. It should be named Map 2.
3. Go to coordinates (62,0) and look at Map 1. Note that your player marker is a pointer as expected.
4. Move 1 block east to coordinates (63, 0). Note that your player marker on Map 1 changes to a dot, even though you are still within the area mapped by Map 1. You have entered the gutter.
5. Look at Map 2. Note that your player marker on Map 2 is also a dot.
6. Move 1 more block east to coordinates (64, 0). Check both maps and note that both still show your player marker as a dot, even though you are now within the area mapped by Map 2.
7. Move 1 more block east to coordinates (65, 0). Note that Map 2 now shows your player marker as a pointer, as expected. You have left the gutter.