Merge request reference in merge commit is not global

Summary

When merge requests are accepted, a reference to the merge request is added to the merge commit message as "See merge request !X"

This is OK when all commits are done on the same repository, but it is non-sense number when a merge request was done within a fork then integrated into the original repository.

When that happens, the link goes to merge request completely unrelated to the merge commit making it completely useless and confusing.

Steps to reproduce

1. Fork a repo
2. Branch and make a change in the fork
3. Create and accept the merge request within the fork
4. Merge that fork into the origin repo

What is the current bug behavior?

The merge request link inside the merge commit message goes to the wrong merge request or to nothing.

What is the expected correct behavior?

Might not be a catch all solution but adding a reference of the merge request id along with the namespace would be sufficient to catch most scenarios within Gitlab.

Output of checks

Haven't tried on GitLab.com but most likely happens.