'yum --security check-update' reports different result between servers.

Issue

• 'yum --security check-update' reports different result between servers as mentioned below. Could you please investigate why it is?
• Here is the result of 'yum --security check-update'. '*' indicates the differences between servers.
• Result of serverl012:

  [root@serverl012 ~]# yum --security check-update
  Loaded plugins: product-id, refresh-packagekit, rhnplugin, security,
                : subscription-manager
  This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
  This system is receiving updates from RHN Classic or RHN Satellite.
  rhel-x86_64-server-6                                     | 1.8 kB     00:00
  rhel-x86_64-server-6/primary                             |  17 MB     00:17
  rhel-x86_64-server-6                                                12455/12455
  Limiting package lists to security relevant ones
  rhel-x86_64-server-6/updateinfo                          | 2.1 MB     00:01
 *4 package(s) needed for security, out of 273 available

 *httpd.x86_64                  2.2.15-30.el6_5               rhel-x86_64-server-6
 *httpd-tools.x86_64            2.2.15-30.el6_5               rhel-x86_64-server-6
 *java-1.6.0-openjdk.x86_64     1:1.6.0.0-5.1.13.3.el6_5      rhel-x86_64-server-6
 *openssl.x86_64                1.0.1e-16.el6_5.7             rhel-x86_64-server-6

• Result of serverl063:

  [root@serverl063 ~]# yum --security check-update
  Loaded plugins: product-id, refresh-packagekit, rhnplugin, security,
                : subscription-manager
  This system is receiving updates from Red Hat Subscription Management.
  This system is receiving updates from RHN Classic or RHN Satellite.
  rhel-6-server-cf-tools-1-rpms                            | 2.8 kB     00:00
  rhel-6-server-rhev-agent-rpms                            | 3.1 kB     00:00
  rhel-6-server-rpms                                       | 3.7 kB     00:00
  rhel-6-server-rpms/primary_db                            |  26 MB     02:43
  rhel-x86_64-server-6                                     | 1.8 kB     00:00
  rhel-x86_64-server-6/primary                             |  17 MB     00:12
  rhel-x86_64-server-6                                                12455/12455
  Limiting package lists to security relevant ones
  rhel-6-server-rpms/updateinfo                            | 2.0 MB     00:04
  rhel-x86_64-server-6/updateinfo                          | 2.1 MB     00:00
 *4 package(s) needed for security, out of 273 available

 *ModemManager.x86_64                0.4.0-5.git20100628.el6  rhel-x86_64-server-6
 *NetworkManager.x86_64              1:0.8.1-66.el6           rhel-x86_64-server-6
 *NetworkManager-glib.x86_64         1:0.8.1-66.el6           rhel-x86_64-server-6
 *NetworkManager-gnome.x86_64        1:0.8.1-66.el6           rhel-x86_64-server-6
 *Red_Hat_Enterprise_Linux-Release_Notes-6-en-US.noarch
                                     5-2.el6                  rhel-x86_64-server-6
 *Red_Hat_Enterprise_Linux-Release_Notes-6-ja-JP.noarch
                                     5-1.el6                  rhel-x86_64-server-6
 *abrt.x86_64                        2.0.8-21.el6             rhel-x86_64-server-6
 *abrt-addon-ccpp.x86_64             2.0.8-21.el6             rhel-x86_64-server-6
  :