I move this from the http://www.gamesas.com/bgsforums/index.php?showtopic=1056321&pid=15329143 thread:
What I forgot to mention in that other thread, but written in a PM to LordBaxter, are two quirks in the feature that adds map markers in the known, but not visited state.
1. MMO only check the player's cell and the adjacent 8 cells, and with cell size of 4000 units, it means that it will never add map markers that are more than 8000 units away. I did this for effectiveness, but it is quite easy to check the next ring of 12 cells if tnoMMO.addDistance is set high (or becomes high when you climb a mountain

2. Map Markers to cities are in the city's worldspace (unless you use a (Better) Open Cities mod), which means that they are not detected by MMO, and thus not added until you come within tnoMMO.revealDistance to the marker. I can try to look for doors within the addDistance, and check for map markers to add in the cells that the doors link to, but I fear those city cells are not being loaded, and thus not possible to check either.