I recently duplicated a map and hung one up in my library. When I went to look at the copy still on hand, it displayed BOTH the green arrow marking - which is what one would see when looking at a map in a sign - AND the white arrow denoting where I am and where I'm looking.

This morning, both maps now only show the green arrow marking, thus rendering my map in hand much less effective since it doesn't show where I currently am.

Also, to 'prove' that it isn't just a duplicate map issue where one is posted in a sign and one is not, I created a different map displaying my keep but never made a duplicate. When I removed the map to update building projects around the keep, it doesn't revert to a white arrow and only retains the green arrow where the sign post had originally been.