BOGO Promotional Item Question

Hello everyone,

We have a situation where we want to give the customer 1 special item at a set price no matter how many the customer buys.

I have set this up, but there appears to be a problem when we make revisions.

Lets say the customer orders 50 each of item 123. As soon as the user saves, the BOGO item appears, which is great. However, if the user modifies the quantity to, 40 each, a second BOGO item appears. Or, say, we add a new item, 456, a bogo item appears again. We only want the bogo appear once per order. This causes the users to delete the extra BOGO items on each others.