Okay, this is a pretty strange bug. On a level that is not zero (tested to work on levels 1 and 2), create a shop and put a passageway in the same room. Set the shop number to something that is not zero, and in the upper left corner of the passageway, you should see an item that corresponds to the shop number. Shop #5 causes the Wooden Sword to appear, for instance.
Passageway/Shop interaction bug(b414)
I believe this is fixed in the next build.