Group/project references are linked incorrectly because comments are cached based on first user who views it
Caused by !911 (merged).
See discussion here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/911#note_1551058
Excerpt:
We shouldn't [cache every comment], what is rendered as a link in Markdown depends on the user's access to other projects and groups.
We're giving up security with the current implementation because users will be able to see referenced groups and projects that they shouldn't.
Partial fix: !1014 (merged)