After Rules met unauthorized gifts remain in cart.

We have 3 gifts available at different purchase tiers. Spend over $300 get X, Spend over $400 get Y & spend over $500 get Z. I have priority set at X = 1, Y = 2 & Z = 3.
It all works when adding to the cart, add 10 products at $33/each with subtotal at $330 in the cart gets X added. If they put 3 more products in the cart then subtotal is $429 then Y is added and X is taken away and so on.

However, if they go to their shopping cart and take those 3 extra products out of their cart then the Y stays and it then adds X as well. So now their cart contains 10 products at $33/each and a subtotal of $330 plus an X and a Y. It doesn’t delete the previous tiered gift.

Have you come across this before? Am I doing something wrong with the Priority in the Rule?