I have a Jenkins installation for which I changed the "JENKINS_USER" and "JENKINS_HOME" (in /etc/sysconfig/jenkins) from the defaults.
When I do an upgrade via yum/RPM, it sets the ownership of /var/log/jenkins back to default user "jenkins" (instead of honoring my JENKINS_USER configuration).

This prevents Jenkins from starting after an upgrade. And since it cannot write to the log file, it may not be easy to figure out what went wrong.