This is already fixed in the Fedora packages, but needs to be done for the EPEL ones as well: http://lists.fedoraproject.org/pipermail/scm-commits/2012-June/806680.html
Thanks for the bug report. Can you try if the scratch build at http://koji.fedoraproject.org/koji/taskinfo?taskID=4898810 fixes your problem? As the description of the patch talks about expat 2.1 and EL6 uses expat 2.0.1 I am not sure this actually helps. If it helps I am happy to release it as an update but if you could test it would be great.
I did my own test build by applying the patch you had for F18, and I can confirm it solves the issue.
jabberd-2.2.14-5.el6 has been submitted as an update for Fedora EPEL 6. https://admin.fedoraproject.org/updates/jabberd-2.2.14-5.el6
Package jabberd-2.2.14-5.el6: * should fix your issue, * was pushed to the Fedora EPEL 6 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=epel-testing jabberd-2.2.14-5.el6' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-EPEL-2013-0226/jabberd-2.2.14-5.el6 then log in and leave karma (feedback).
jabberd-2.2.14-5.el6 has been pushed to the Fedora EPEL 6 stable repository. If problems still persist, please make note of it in this bug report.