This is a problem I have not encountered before and I wonder if anyone has any ideas?

I have added some dialogue to an existing NPC (Doctor Lesko). Note: added, no existing dialogue has been changed.

I have not altered anything in Lesko's shack nor have I altered anything about Lesko himself.

I can go to the shack and talk to Lesko and my dialogue works properly. I can enter and leave the shack without problems. I can save in the shack and re-load as many times as I like without problems.

However: if i exit the game then try to re-load from a save made in the shack the game crashes, without fail. Any save made in the shack, be it auto, quick or otherwise will cause a crash. I can load a save made before going into the shack and go in without any trouble, and I can load a save made after going into the shack, talking to Lesko and coming back out again.

I've tried going back to a completely clean save, and I've tried cleaning any 'identical to master' records from the .esp/.esm using FO3Edit, but the problem simply won't go away.

This is really annoying me as it simply makes no sense. Does anyone have any clue what might be causing this?