In diff_menu_alter() the access callback is changed for the 'view' revision links. This becomes a problem when diff is disabled on a content type.
The diff callback does check 'administer nodes', but that's not enough, normal users should also be able to use this when they have this permission, diff enabled or not. And that still does not solve the problem, because the rendering of the view revision links and the 'view revision' button are both using the same function.
Install Drupal core, diff, workbench, workbench moderation to really enjoy this problem.
Closed: outdated
3.0
Code
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.
Given the proximity of EOL for Drupal 7, marking this as won't fix. The likely final Drupal 7 release of diff has landed in https://www.drupal.org/project/diff/releases/7.x-3.5 → . If this is something still applicable to a more modern version of the module, feel free to re-open and post additional notes.