Callback called when an authorization is revoked.

Hi,
if I remove an automatic payment form the Sandbox app (withdrawal of authorization) I've seen that you call again the callback used to confirm authorization.

It seems to me that only the token is passed and no other parameters. Is this so or am I wrong?
I don't see any difference between this call and the one made after the token was created.
How do I distinguish the two calls?

Thank you very much

cld