Oh phew, thought the blank interiors was my GPU's doing (user-end error would be a sheer impossibility of course ). Hopefully the issues get fixed!

This problem's been getting on my nerves too, and it's happend in my own cells after I've optimized them with room and portal markers. It seems that moving the markers out of the way is indeed the best fix for now. I rigged up an AutoHotkey script to help make that process quick, precise, and automated.

It's demonstrated here:
http://www.youtube.com/watch?v=TP21lHSg1-o

You can download it as a standalone exe here (no malware, I pinky promise):
http://awforsythe.com/files/nvgeck_roommarker_v1.exe

The script will run in the background and can be closed from its tray icon. Just press Ctrl+Shift+R to start the process of moving room markers. If you have http://www.autohotkey.com/ installed, you can just download the script file (and modify it all you like, if you so choose):
http://awforsythe.com/files/nvgeck_roommarker_v1.ahk

Edit: I've also just discovered http://www.gamesas.com/index.php?/topic/1148040-how-to-fix-lighting-havok-and-rendering-issues/, which seems like an actual, effective fix for this problem. Never mind this post then!

This thread has been dead for several months till today, but a much simpler solution has been posted in http://www.gamesas.com/index.php?/topic/1148040-how-to-fix-lighting-havok-and-rendering-issues/. It is also now mentioned in the pinned installation FAQ. (EDIT: you edited while I was posting. Double never mind.)