Just decided to film it. It shows up at around 20 seconds.
Just recently switched to TOPDOWN_MAP and am remapping everything in a new map file and noticed that this was happening. Random turfs would come over top of buildings... I don't know how nor why. Anyone else had this happen?
EDIT: Also I've noticed some things change layers or something whenever you go past them at different angles. Like the Suna Symbol, is generally above the house, but it goes below the house when your looking it from a different direction or the sand covers a part of the symbol... thing is... all the buildings have the same layer structure. layer=MOB_LAYER+1