The bug
When using a normal map (not an explorer map), the white circle indicating the relative position of the player disappears after a certain distance instead of becoming a smaller white circle.
Tested with both normal maps and explorer maps. The small white circle works appears normally on the explorer maps, but not on normal maps.
How to reproduce
Get a new map; right-click
Move away from the plotted area for a while
The marker turns into a dot
Keep going, and you will see it disappears rather than shrink
Confirmed for 1.13.1.