Why does CLOSE_WAIT connection remian on ldap for a long time ?

Issue

Some CLOSE_WAIT connections on ldap remain for a long time like below.

# netstat -ap|grep idms
tcp       76      0 znews-l003.t.rd.aaaa:27175 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  15708/httpd
tcp       76      0 znews-l003.t.rd.aaaa:11781 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  7139/httpd
tcp       76      0 znews-l003.t.rd.aaaa:11783 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  7138/httpd
tcp       76      0 znews-l003.t.rd.aaaa:11782 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  7140/httpd
tcp       76      0 znews-l003.t.rd.aaaa:11785 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  7142/httpd
tcp       76      0 znews-l003.t.rd.aaaa:11784 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  7141/httpd
tcp        0      0 znews-l003.t.rd.aaaa:54275 idmst5.t.rd.aaaa.com:ldap  TIME_WAIT   -
tcp        0      0 znews-l003.t.rd.aaaa:54274 idmst5.t.rd.aaaa.com:ldap  TIME_WAIT   -
tcp        0      0 znews-l003.t.rd.aaaa:54277 idmst5.t.rd.aaaa.com:ldap  TIME_WAIT   -
tcp        0      0 znews-l003.t.rd.aaaa:54276 idmst5.t.rd.aaaa.com:ldap  TIME_WAIT   -
tcp        0      0 znews-l003.t.rd.aaaa:53834 idmst5.t.rd.aaaa.com:ldap  ESTABLISHED 3070/automount
tcp       76      0 znews-l003.t.rd.aaaa:46757 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  3225/mysqld
tcp       76      0 znews-l003.t.rd.aaaa:46756 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  3143/ntpd
tcp       76      0 znews-l003.t.rd.aaaa:46758 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  3322/xfs
tcp       76      0 znews-l003.t.rd.aaaa:38645 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  11540/httpd
tcp       76      0 znews-l003.t.rd.aaaa:38644 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  11537/httpd
tcp       76      0 znews-l003.t.rd.aaaa:38646 idmst5.t.rd.aaaa.com:ldap  CLOSE_WAIT  11541/httpd