Problems with extending CI_Form_validation

That I didn't spot this from the start :S

It's your class name AdvancedValidation. This is not autoloaded, so your rule is not available. That is why it is returning FALSE.
When not available, you won't get a PHP error or warning for a non existing method as the validation class uses a method_exists check on called rules.

Also this is not how the Loader class works when loading extended classes.
Look at the Loader class for more details.

If you don't want to use a Class prefix then the class name should be Form_Validation

So rename the class (I would do this),
or manually load the extended class (which is going to cause more problems than solve them)