Description of problem:
The current sudo package attempts to add a line to nsswitch.conf if it is missing but it fails it can fail if the update transaction also includes glibc on a multiarch system.
What happens is that due to the multiarch nature two glibc packages will be installed and in some circumstances yum orders the updates in a way that first glibc is updated, then sudo (at which point the added line exists in /etc/nsswitch.conf) and then the other glibc arch is updated which overwrites /etc/nsswitch.conf with the copy included in glibc.

Version-Release number of selected component (if applicable):
sudo-1.7.2p1-14.el5_8.3.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Install a fresh rhel 5.8/x86_64 with sudo and openssl and no updates
2. remove the 'sudoers:' line from /etc/nsswitch.conf
3. yum update sudo openssl glibc

....  
Running Transaction
  Updating       : glibc-common       1/14 
  Updating       : glibc              2/14 
  Updating       : openssl            3/14 
  Updating       : sudo               4/14 
  Updating       : nscd               5/14 
  Updating       : glibc              6/14 
  Updating       : openssl            7/14                
....

Actual results:
# grep sudoers /etc/nsswitch.conf
#

Expected results:
# grep sudoers /etc/nsswitch.conf
sudoers:  files ldap
#


Additional info:
The example with 'sudo openssl glibc' is just one easy way to provoke this issue. Any combination of updates that can trigger sudo being updated in the middle of a glibc multiarch sandwich could cause this problem.