I'm having the same problem with NPCs trying to walk through the walls where Thievery puts its Tools of Magica shop, and editing pathgrids in the CS is something that scares me...
EDIT: Found out it really did screw up things, so I opened it in the CS and after much cursing and swearing I was able to remove the pathgrid nodes from where Thievery puts its two shops, hopefully without breaking anything.
I admire real modders for having the balls and the patience to use the CS. Me I'm always a nervous wreck, fearing it will crash when saving or it will add all sorts of things to the ESP (adding dialogue is especially "popular").
BTW, there is also a minor pathgrid conflict with the http://www.planetoblivion.de/index.php?option=com_content&task=view&id=1341&Itemid=73 which puts a vendor outside The Best Defense.
An while I'm at it I may as well mention a minor problem with MMM, as discussed http://www.gamesas.com/index.php?/topic/1109315-relz-map-marker-overhaul/page__view__findpost__p__16546093