Well first, this isn't part of fungal lake, its a seperate unrelated .esp (Though I imagine I should set up the worldmap to fungal lake as well).
Second, I think I need to send it to you, cause I already [censored] around trying to make the connections myself. I'll tesfiles it, zip it, and e-mail it.
Basically what happens is when you go in a worldspace, it sets your world map. So when you go into Tamriel, it sets the worldmap to Tamriel. Any time you go into an interior, it freezes the map and map location.
So when you went from Tamriel into the underdark, it considered you inside a Tamriel dungeon still, freezing the Tamriel map in place. So no matter how far you went in the Underdark, you'd be in the same exact location on the Tamriel map.
What I was trying to do was take every ENTRANCE to the underdark (no need to do exit-onlys), and slide a transition cave between the doors.
The transition cave is a cave built in the UnderdarkWorld (worldspace) with the underdark map assigned. The cave itself is only a few pieces, very small (but could be expanded).
So by making the player go (briefly) through this extra cave transition, it updates the map real fast, setting it to Underdark.
I've got all the needed cave transitions set up in the worldspace, but the doors are [censored].