I have posted
this question on StackOverflow 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.