I have had a similar bug where I've set the buy/sell items for a city, but after saving the map and going to it properly, all of the items are gone and the city essentially sells or buys no goods. This happened on a map I started developing but ended up abandoning due to a lack of interest in Pharaoh at the time.
The only thing I could see as a fix is to reset the map and start over, or to simply set other items for that city.
If my memory is serving me right, this happened when I had set up some cities on the map (simply by deleting many of the icons from the Default map to set up my "Empire" of that map), then added a new city on the empire map through the button at the bottom, which seemed to corrupt one of the other cities, forcing me to have to "rebuild" the Empire Map by using the Reset button to get all the cities back on the map and going through the same process again. Do be aware that I can't remember exactly what I did, since this was some years ago when it happened to me.
It is annoying and irritating when it happens though!
[This message has been edited by Sajuuk (edited 10-03-2015 @ 03:14 AM).]