Planescape Torment problem/glitch

[Melusine]

I've encountered a problem or possible bug in Planescape Torment, so I wonder if anyone else knows about this.

I've never completely played through the game (that's what I hope to do now), but I did complete a part of it several times. Every time when I went to get the Bronze Sphere for Pharod, I cleared out the catacombs completely, so I entered both the city of the Silent King and the Warrens of Thought and did Hargrimm's and Many-As-One's quests. Of course, when you enter the cranium rat area, you are made prisoner after your talk with Mantuok and have to kill all (were/cranium)rats to get out. I don't know if there's another way to do it, always played it this way.
Anyway, this time through, I never entered the Warrens at all when I retrieved the sphere.

Then, later, Morte was stolen from me in the Lower Ward and I had to get Lothar a skull to get him back. I thought I'd try things this way for once, talk to Mantuok for the first time below Lothar's house and see what changed when I entered the Warrens of Thought (maybe they wouldn't be initially hostile now, especially since I might be able to tell Many-As-One that Mantuok was also working for Lothar).
But the problem is, whenever I try to enter the Warrens, my game crashes.
I've had similar crashes upon loading an area before, but I wonder if this one has anything to do with the fact that I first talked to Mantuok below Lothar's kip rather than in the Warrens.
In one save game, I fed Mantuok the poisoned cheese and killed the were-rats before proceeding, in the other I left him alive, but in both instances my game crashed when I tried to enter the Warrens of Thought. My game's pathed by the way.

Anyway, my question is: has anyone else ever tried doing the quest this way? Please don't spoil as to what happens when you enter the warrens, just let me know if it can be done or if there's a bug that makes it impossible to enter the Warrens for the first time at this point in the game.

Thanks in advance!