When I run in to the store (for example) to lose zombies or to switch to my pistol and take them out. I run through the front entrance and in to the back of the store and set up my shot. I anticipate the zombie walk through the doorway i just had to walk through, but it seems they prefer to walk through walls instead. I have also noticed (only in the store, not sure about other places) that some zombies do not walk up the steps to get in to the store, so they are in the building only to their waist-up. One more thing i'd like to mention is that most zombies don't know how to walk up stairs, except the one that killed me by clipping me through a wall.