It has been a while since I used the editor, but I remember having the same problem at first. My solution was to do the following:
- Using the "Easy-Add" option above the tabs for the item type. It will add the selected quantity with a meaningful timestamp.
- Just use a Quantity of 1 for accessories! If you want multiple of the same kind, then add multiple entries with a Quantity of 1 each.
Unfortunately, your tip did not work....I set the quantity to 1 for each entry but all three still assign to Rex when equipped.