@kiyama,

if you are an admin or have the access the galleries will not ask you for a password, all other users will be presented with the login form.

if you want to disable the behavior add this code in your functions.php file or in a plugin.

function mytheme_remove_ims_actions(){
global $ImStore;
remove_action( 'the_post', array( $ImStore, 'bypass_protected_galleries' ), -1 );
}
add_action( 'wp', 'mytheme_remove_ims_actions', 300 );