When I add a specific user in a secondary group, it has no effect. Other users with the exactly the same user group configuration have not this problem.
This is an issue that, if it happens, disabling add-ons won't fix it because it has broken the cached value. If rebuilding user caches fixes it, then it's definitely caused by an add-on.
I have noticed that setting View attachments to posts to non registered doesn't apply. I have rebuilt the forum information cache and the problem persists.
Rebuilding caches didn't fixed the view attachments for unregistered problem. When I disable all addons unregistered users still can't view full attachments.
Last addon I installed was Zodiac icons, anyway I think I have this problem before.