At one point, they were drawing tiles, the walls associated with them, objects, etc...

Moving objects would end up between tiles and the sprite would be cut off by a different tile draw. Worse, there was no sort order that worked for all cases. They ended up creating, what the speaker called "an ai" to move the object away from the draw conflict, get it all drawn, then move the player back, just ahead of the actual motion...

In hindsight, they could have just decoupled the walls from the tiles and it all could have been a lot simpler!