Comment 4 for bug 1404616

The 2.8 help was added to vivid, so this is no longer a problem in the latest Ubuntu release.

https://launchpad.net/ubuntu/+source/gimp-help/2.8.2-0ubuntu1

As regards trusty, a backport to update gimp-help to 2.8 would be a proper step to take for someone who is willing to do it.

https://help.ubuntu.com/community/UbuntuBackports