The patient is fine, and is resting comfortably. It does not appear to have suffered for our addition of code. HP-UX clients are burbling along happily, as are all the bajillion others.
A postmortem of how this slipped through showed that HP-UX clients running Connectathon ( http://www.connectathon.org/ ) work just fine against the unpatched CentOS. Something about Connectathon does not use the same code path to create a file that the regular HP-UX utilities do. Since we do not have source to HP-UX, we can not even begin to guess what that is. Bottom line: Connectathon certification of a new NAS server is now no longer sufficient: We will need to do some manual certification too.
The good news is that now it acts just like is should. Quiet, no trouble, acting like a cluster should and failing over things when it ought to. We'll let it cruise along a bit longer and then migrate a few more things to it.