No, it's just a bug. I have been using two sets of data where the name of the countries were not perfectly matching (example: United States VS United States of

No, it's just a bug. I have been using two sets of data where the name of the countries were not perfectly matching (example: United States VS United States of America). I fixed most of the inconsistencies and showed the map to some people to help me spot the problems. This one slipped through (as the geocoding of Serbia and some NaN).