Comment 3 for bug 651537

 There are at least four "bugs" here:

1. Pam doesn't do the hack to make sure coreutils is installed first.

2. Yum in 5.3 fails the transaction when scriptlets fail.

3. rpm marks %post failures as a scriplet failure.

4. rpm changes it's ordering of pam/coreutils, which without #1 it is entitled to do.

...the way this was "fixed" in Fedora was to have rpm not mark the transaction as a scriptlet failure when %post fails (fixing #3). One way to fix it for 5.3 is to fix pam (I know some people rebuilding CentOS have done this), which takes care of #1. And the other work around is:

http://lists.centos.org/pipermail/centos/2009-April/075092.html

...which fixes #4. Reverting #2, which I assume is what you want given where you opened the bug, is possible ... but the least preferable IMO.
 I'll pass this over to Panu to see if he wants to do #3 for 5.4.