Enabling external issue tracker breaks referencing internal issues from other projects

Summary

Enabling external issue tracker breaks referencing internal issues from other projects when the reference is typed in, but not when the link is pasted.

Steps to reproduce

1. Create project-a in your personal namespace
2. Create issue 1 in project-a
3. Create project-b in your personal namespace
4. Enable JIRA service in project-b
5. Create a merge request 2 in project-b
6. Post project-a#1 as a comment
7. The text is not transformed to a link
8. Paste https://gitlab.com/your-user-name/project-a/issues/1 as a comment
9. The text is transformed to a link

Example Project

adamniedzielski/test-project-3!1