Project custom field applied to departments rbs

Dears,

I created project custom field of type lookup and in Department field i selected Human Resources as below screen

I used this field in Project Information Page. this field supposed to appear in any project belongs to Human Resources RBS Departments. But it appears only when i select Human Resources Department

So, my questions is Why custom fields doesn't appear in sub-departments under Human Resources?

Any Help

Regards, Mohamed Abdel Ghaffar | http://sharepointfoundation2010.blogspot.com