Clarification about MY_Controller and relative inheritances

But, if MY_Controller does not mess with any CI_Controller properties (and it only has one - private static $instance; so there is nothing to mess with) then technically he does not need to explicitly call the base class constructor. PHP will do it anyway.

That is true, but in that case the MY_Controller class may not have a __construct() method. If it does have a __construct() method you MUST call the parent::_construct manually.

So the question is:
Does @gbwebapps have an empty constructor in his MY_Controller class?