Why are a few UIDs are mapped as 4294967294 on a RHEL7 NFS client, from a RHEL6 NFS server?

Issue

• An NFS share is mounted from a RHEL6 server onto a RHEL7 client machine.

• Why are some of the UIDs are mapped to the number '4294967294'?

  # ll /home/hs/sysadm/
  total 72
  drwx------.  5 4294967294  sysadm      4096 Sep 28  2011 user1/
  drwx-----x.  8 4294967294  sysadm      4096 Aug 30  2012 user2/
  -rw-------.  1 user9       root          44 Sep 28  2011 user3
  drwx------.  2 nobody      4294967294  4096 Mar 26  2010 user4/
  drwx------.  8 4294967294  sysadm      4096 May  7  2008 user5/
  drwx-----x. 52 user6       sysadm     12288 Feb 14  2013 user6/
  drwx-----x. 11 4294967294  sysadm      4096 May 28  2012 user7/
  drwx-----x.  9 4294967294  sysadm      4096 Jan 31  2012 user8/
  drwxr-xr-x. 85 user9       sysadm      4096 Feb 13 15:40 user9/
  drwx-----x.  8 user10      sysadm      4096 Aug 30  2012 user10/
  drwx-----x.  9 4294967294  sysadm      4096 Jun  6  2013 user11/
  drwx------. 10 4294967294  sysadm      4096 Apr  5  2011 user12/
  drwx--x--x.  3 nobody      sysadm      4096 Dec 17  2008 user13/
  drwx--x--x. 62 user14      sysadm      4096 Feb 12 15:57 user14/
  drwxr-xr-x. 29 4294967294  sysadm      4096 Jan 22 14:24 user15/
  drwx-----x.  8 user16      sysadm      4096 Aug 30  2012 user16/
  

• The same NFS share while mounted on a RHEL5 system:

  # ll /home/hs/sysadm/
  total 72
  drwx------  5 user1     sysadm      4096    Sep 28  2011 user1/
  drwx-----x  8 user2     sysadm      4096    Aug 30  2012 user2/
  -rw-------  1 user9     root        44      Sep 28  2011 user3
  drwx------  2 110       user4       4096    Mar 26  2010 user4/
  drwx------  8 user5     sysadm      4096    May  7  2008 user5/
  drwx-----x 52 user6     sysadm      12288   Feb 14  2013 user6/
  drwx-----x 11 user7     sysadm      4096    May 28  2012 user7/
  drwx-----x  9 user8     sysadm      4096    Jan 31  2012 user8/
  drwxr-xr-x 85 user9     sysadm      4096    Feb 13 15:40 user9/
  drwx-----x  8 user10    sysadm      4096    Aug 30  2012 user10/
  drwx-----x  9 user11    sysadm      4096    Jun  6  2013 user11/
  drwx------ 10 user12    sysadm      4096    Apr  5  2011 user12/
  drwx--x--x  3 152       sysadm      4096    Dec 17  2008 user13/
  drwx--x--x 62 user14    sysadm      4096    Feb 12 15:57 user14/
  drwxr-xr-x 29 user15    sysadm      4096    Jan 22 14:24 user15/
  drwx-----x  8 user16    sysadm      4096    Aug 30  2012 user16/
  

• On the RHEL6 NFS server:

  # cat /proc/net/rpc/nfs4.idtoname/content | grep test
  test.example.com group 12 mail@example.com
  test.example.com user 1823 user12@example.com
  test.example.com user 110 nobody
  test.example.com group 110 user4@example.com
  test.example.com group 1004 www@example.com
  test.example.com user 0 root@example.com
  test.example.com group 0 root@example.com
  test.example.com group 1000 sysadm@example.com
  test.example.com user 1887 user9@example.com
  

• Why are some of the uids mapping fine, while others are not?

• All uid/gid come from a single LDAP server via sssd, for both NFS client and server.