I have noticed this on one of my four toons that has been to Solstheim.

When I open the map there is usually a small square around my character's location marker that is not rendered on the map. It is a square with about 1.5x the length of the character marker on the diagonal.

The square will just look like water, and has sharp edges.

The character I've noticed it on: Orc, 90hrs level 35, created on patch 1.2 (iirc)

I have also noticed this after installing dragonborn. It happens mainly on Solstheim, and sometimes (but rarely) it happens in skyrim. It doesn't happen everytime, only at random. It doesn't really bother me, but it makes it look like my current location is in a square lake haha After Hearthfire and Dawnguard, the frequency of this square appearing decreased but it still happens.

16 MB save, 183 hours, Level 81 Nord with all trophies (including DLC).