Hashed password used as salt in crypt() function

Question

I don't understand why using $old_password in $new_password = crypt($password, $old_password) generates the same echo results for $new_password and $old_password at the bottom of the following code.

I would be thinking that we need to use some kind of salt as the second paramater and not the $old_password (already encrypted one).

    $password = "secret"; // Usually from a form
    $format = "$2y$10$";
    $salt = "iusesomecrazystrings22";
    $format_and_salt = $format . $salt;

    // Initializing Values
    $old_password = crypt($password, $format_and_salt);
    $new_password = crypt($password, $old_password);

    echo $new_password; //will echo $2y$10$iusesomecrazystrings2uVot5BCtPGBrRuQch85uTPr2L2fKlh0y
    echo "<br>";
    echo $old_password; //will echo the same as above $2y$10$iusesomecrazystrings2uVot5BCtPGBrRuQch85uTPr2L2fKlh0y

I was experimenting with the code and I went over the php.net manual and google.com results.