Ah yes, the 4000/C000 thing is definitely Isaac's direction. Looks like if you're approaching a transition screen the game records Isaac's direction when transitioning to maintain that after the transition. Although, some transitions fix Isaac's direction (e.g. world map doors) and that data gets overwritten.
Looks like other highlighted areas are related to the position of the camera. I tested it in a dungeon (because sometimes world map/dungeons behave differently) and got the camera to lock somewhere else. I'm guessing that near transition zones like doors there is an area around them which takes control of the camera as you move through the area, as opposed to locking the camera on Isaac. That way you can control the camera movement as Isaac goes through a door (which is slightly irregular).
I bet that camera lock in tret is to do with the number of breakable leaves in the dungeon.
Looks like other highlighted areas are related to the position of the camera. I tested it in a dungeon (because sometimes world map/dungeons behave differently) and got the camera to lock somewhere else. I'm guessing that near transition zones like doors there is an area around them which takes control of the camera as you move through the area, as opposed to locking the camera on Isaac. That way you can control the camera movement as Isaac goes through a door (which is slightly irregular).
I bet that camera lock in tret is to do with the number of breakable leaves in the dungeon.