Extending Controller?

[eluser]iConTM[/eluser]
I just can't figure out how to extend the controller class properly in CI

Let's say I want to have the following tree:

Code:

// ./system/libraries/
Controller

// ./application/libraries/
MY_Controller extends Controller

// ./application/controllers/
ControllerA extends MY_Controller
ControllerAa extends ControllerA
ControllerAb extends ControllerA

ControllerB extends MY_Controller
ControllerBa extends ControllerB

It works fine until level 3 (ControllerAa, ... )

Is this possible in CI?

regards