Board Thread:The Last Sovereign Discussion/@comment-27713488-20171109041048/@comment-31763506-20180522135648

Sotter:

There's a problem with underlying script that switches out the walls, floors, carpets, etc., which is called TileSwap and was developed by an RPGMaker scripting geek named Hime. So the bug is not something SL can easily fix. I've worked out what the problem is, but have put going in and fixing it pretty low in my list of priorities.

Basically, the game renders maps as collections of individual tile types, and has some fancy rules for dealing with edge tiles in places where passages through vertically oriented walls occur. TileSwap replaces one style of tiles with another, and just assumes that the edge of any area of tiles is the outer perimeter of all tiles of that type. There's a similar problem with the way TileSwap handles bodies of water meeting waterfalls.