I have posted this question on StackOverflow
<http://stackoverflow.com/questions/24111890/org-mode-require-org-publish-causes-downgrade-in-org-version>
but in case you don't want to visit the page, I've pasted the contents in
this email.

I have just upgraded org-mode to the latest available in ELPA. According to
the official documentation, the installation has to be done in fresh emacs
session where no org-related scripts/files have been loaded. The
installation is successful, and org-version reports that I have updated to
8.2.6 (from 7.9.3f). However, as soon as I put back my old org-related
scripts, and reload emacs, I'd get 7.9.3f when I run org-version. To track
what's causing it I retrace my steps by adding my org-related scripts one
by one. I found out that when I add back (require 'org-publish), the
version downgrades to the built-in one. I don't know why this is happening.

Thanks.