As a DM i'm running Dungeon of the Mad Mage and a few other games. Then players can see an area using their vision my DM ability to see the gid lines disappears in that area the players enter as well as the discs with room numbers and any monsters the game has on the GM info overlay layer all disappear so I end up forced to drag players tokens out of the rooms so I can move the monsters onto the token layer and the like. Also certain NPC's and lights in the scenes create odd black circles of darkness players can't see into even though it doesn't make sense.