Max uses not respected

I trying to apply a money off discount to a single product that can only be used 50 times in total.

My settings are:
QUALIFICATION TYPE:Minimum quantity
MINIMUM QUALIFICATION AMOUNT: 1
Required products: No specific product
DISCOUNT TYPE: Fixed amount off per qualifying item
DISCOUNT AMOUNT:2
Discounted products: the appropriate product is selected.
MAXIMUM APPLICATIONS:0
MAX USES: 50
MAX USES PER USER:0
MAX USES PER CODE:0

This discount is applied ok, but once it's been used 50 time the discount is still applied, however using the max uses per user is respected.