Losing items in an item shop

In my triggers I have it so that when an item is sold from this shop, the item being sold is removed and and another item is added (So that there are only ever a maximum of 5 items being sold at a time by this shop). The problem is that if an item isn't sold and is sitting in the shop while other items are being bought it will disappear. It doesnt disappear randomly either, it will disappear immediately after another item is bought. I am almost sure that this isnt a result of some missmatch in my triggers because I tried this with many item combinations. Why are these items disappearing?!?

plz post ur triggers so we can c whats wrong with it.

Event:
A unit uses an Item
Action:
If: Item-type equal to (Custom Item 2)

Then: Unit - Remove Ability 1 to triggering unit

Unit - Add Ability 2 to triggering unit

Neutral Building - Remove (Item-type of item being manipulated) from random unit owned by player(owner of triggering unit) of type (custom unit)
Neutral Building - Add (Item-type of Custom item 3) to random unit owned my player(owner of triggering unit) of type (custom unit)

Basically there are 5 levels for about 90 spells and this is the trigger to upgrade the spell from lvl 1 to lvl 2.