Mentioning issue number in merge request or issue no longer cross-links it to mentioned issue

Summary

When mentioning an issue number (#123) in a merge request, the issue is no longer cross-linked and is not listed as a related merge request. However, if you mention the merge request number (!456) in an issue, then that merge request is cross-linked and is listed as a related merge request.

In other words, you broke the feature that I added to GitLab. 😦

Steps to reproduce

1. Create an issue
2. Create a merge request
3. Mention the issue number from step 1 in the merge request (either the description or in the comments)
4. Go to the issue and notice there is no cross-link comment and no related merge request listing

What is the current bug behavior?

Mentions of issue number in merge request do not cross-link and do not list the related merge request.

What is the expected correct behavior?

Mentions of issue number in merge request should cross-link and should list the related merge request.

Relevant logs and/or screenshots

Will use this issue as an example.

Output of checks

This bug happens on GitLab.com

Possible fixes

Checkout my original commits perhaps: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1991