Thanks Ned and Nico.
Yes, "yum downgrade dokuwiki" says there is nothing available. I can rebuild version 20091225.c from dokuwiki.org, but I don't know if there where any patches added by Epel, and this is likely.
My guess is the source rpm for Epel was the same as the source rpm for Fedora, so I am going to try this one.
I will be more careful with packages coming from other repos than CentOS...
Thanks again,
-- Philippe
EPEL uses koji.fedoraproject.org to build the packages so the source and binary rpms are on koji.
http://koji.fedoraproject.org/koji/buildinfo?buildID=151881
Regards Neil