Just decided to film it. It shows up at around 20 seconds.

Problem description:
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

If the building turfs are all big icon, they should be pulling themselves forward of other turfs on the same layer; it is possible that something is interfering with that or there's an imperfection in the algorith, but I'd need a demo to see more. The last time I looked into an issue similar to this I found that the big icon was an underlay of the turf and was not actually using the pull-forward behavior as a result, and this was not a bug.

The safest course of action is to make sure the big icon has a higher layer than anything else. I'm not sure what the layer of the symbol is, although I'm also not sure what the symbol is so I didn't know what to look for in your video.
In response to Lummox JR
The symbol was the hourglass that appears halfway under the house... A demo you say? I'll see what I can produce... I'll send you link by pager.