supplier site not defaulted from standard operation into work definition when not referenced

A standard operation(osp operation) has supplier and supplier site defined in it. when this OSP operation is defined in a work definition, the supplier , supplier site gets defaulted when reference option is selected. But when reference option is removed, atleast supplier option is appearing, but supplier site is not getting appearing. It is empty. Why is not supplier site appearing same as supplier option when reference is not selected ?