I just finished a session with the GECK, and while attempting to add a sleeping pallet to the flat stone area behind where Joshua sits I discovered that the Angel Cave cell was almost completely blank except for the upper exit archway. In fact, this applied to pretty much any cave interior cell I pulled up in the render window, much to my disgust. All that rendered when I pulled up Angel Cave were the two Dead Horses that wander around the lower portion of the cave and some markers (M).

At first I thought it might be because I have a character saved standing in Angel Cave, but then I pulled up some other cave cells and the same thing happened, so that's not the problem. I do have the most recent version of the GECK, so that's not it either.

I was wanting to add said pallet and remove the 'owned' tag on the two crates against the cave wall there, but that's hard to do when I can't see anything.