In a single frame the world map gets colored only around the player
You can see the effect making a script like this one:
coc "10,15"
coc "10,16"
coc "10,17"
coc "-5,-5"
and start the game with openmw --skip-menu --script-run <full path to script> --start '-5,-5'
Once the game started you'll see that the map shows the cells in the north west as visited but without the proper coloration. One has a similar effect the last coc is in a interior.
If the last coc is nearby the others, the map gets colored properly.