Flex-field security rules created with Parent Values

 Hi,

     I have created flex field security rules for a cost center segment. The values in the rule are parent values with only include values.

     Moreover, the parent values are 3 digits and the child values are 4 digits. The hierarchy level security rules are not working despite the value set was created with Hierarchial security and the segment has security enabled. It is not working.

     Please suggest what are the known short comings in Parent level security rules.

Regards,

Prabhu