[Typo3] Template on next level starts from one level deeper?

[Bing Du]

I created two root level templates, tempA and tempB.  I want only the 
frontpage to use tempA and all other pages use tempB.  So I set tempB as 
template on next level for tempA.  I thought SITE would use tempA and 
the rest pages should use tempB.  However the actual result is SITE, 
Overview and Departments all use tempA.  Policises, News, Dept1 and 
Dept2 use tempB fine.

Page tree:
-------------
SITE
   Overview
     Policies
     News
   Departments
     Dept1
     Dept2
--------------

The question is why Overview and Departments use frontpage template 
(tempA) rather than subpages template (tempB)?

Where should I check?

Thanks in advance for any help,

Bing