Earlier bug re-introduced – can keep adding more than max?

I saw that this was closed in 1.4.3; I’m not on 1.5.1. To reproduce:

– Set max quantity on item (in this case, 6)
– Add 6 of said item to cart (works fine, as expected)
– Add 6 more of said item to cart
– Receive error: “You can add a maximum of 6 [item] to your cart. You already have 6.”
– Cart now contains 12 items
– Add 6 more of said item to cart
– Receive error: “You can add a maximum of 6 [item] to your cart. You already have 12.”
– Cart now contains 18 items

Checkout completes fine with the more-than-maximum number of items. User can add tickets indefinitely.