[eluser]CroNiX[/eluser]
Normally you'd be correct, but MY_Controller is a special case. See the userguide I linked to in my first post about extending the core of CI. Since he didn't capitalize it correctly, CI couldn't find it because it specifically looks for "MY_"
Just like whenever CI loads Input, CI looks to see if you extended it with MY_Input. It looks to see if you extended the router with MY_Router, etc.