After modifying system-auth as you suggested ( I removed the ldap definitions from system-auth and reordered the sssd definitions),
and caching is working now. Thanks for your help.
If I don't comment ldap_pwd_policy = shadow line I got below errors even I have ShadowExpire and ShadowLastChange attriutes set.
(Fri Nov 18 16:00:14 2011) [sssd[be[
ldaptest.jazzythemartian.com]]] [find_password_expiration_attributes] (1): No shadow password attributes found, but shadow password policy was requested.
(Fri Nov 18 16:00:14 2011) [sssd[be[
ldaptest.jazzythemartian.com]]] [be_pam_handler_callback] (4): Backend returned: (3, 4, <NULL>) [Internal Error (System error)]