Ok, I've had this problem in the past, but I thought I had figured out how to fix it. Now I'm having it again.
As soon as the player enters an area, she can see the entire zone, or most of it. Basically, it's acting like it's an outdoors area, and revealing all terrain within a certain distance. Walls and doors aren't blocking vision of terrain (though they do sometimes block visibility of npcs).
Now the last time I had this problem, it was because I had the Terrain Type in Advanced Area Properties set to "Exterior". That isn't the case this time. I have it set to "Interior, Artificial, Underground". It's in the Drow Interior tileset, and the only Hakpak I'm using is Project Q.
Any ideas?