Similarly, changing a customer's address is typically
idempotent, because the final address will be the same
no matter how many times it is submitted.
So, even if in one case there's an internal state change (going from an old address to a new one) whereas in the other there is not (going from the new address to the new one again), it is commonly considered idempotent because the end result is the same.
[1] http://en.wikipedia.org/wiki/Idempotence#Computer_science_me...