Since when can you only pick up one?
To test this, I added 3 to my cart... and it worked. So...
If you proceed to checkout, you eventually get an error that something is wrong with your order. It then proceeds to only allow you to purchase one. Sucks. :( Wanted to get two copies for co-op and now we have to make separate orders. Meh.
Still a great deal. Thanks OP.