Mbertu on "Saving option for the first time"

Hi everybody, I'm Michele from Italy. I've a question about the saving option's process.
Both in my plugin and my template I've found a problem. The first time an option is saved the validation callback passed to the register_setting funciton is triggered twice.
First time the input variable have the post fields values, the second time have the output of the first callback execution.
Is this normal?