sometimes i get 'em free, sometimes i gotta pay

I present to you a moral dilemma:

If you order coffee at a coffee establishment that gives free refills, and the nice lady does not charge you for said coffee because she was installing a debit card machine and you volunteered to be the guinea pig, is it acceptable to request a refill on your free coffee?

In other words - have you gratuitously received the individual receptacle of coffee, or have you gratuitously received the equivalent to what you would have otherwised paid for, which would be the individual receptacle of coffee, as well as a future interest (possibility of reverter) in a refill?

Also, if you choose to not pursue the refill, and you are left with an empty coffee receptacle, and you put a house in that coffee receptacle, is it still a coffee receptacle?