Issue search by number is broken

Summary

In previous versions I were able to search for issue with strings like #345 so I were able to find issues based on their number (given the fact the auto-generated branches always show the issue number).

Steps to reproduce

Search for any issue using their number, like #345, when in a specific project (as you can see from the following screens. I'd like to point out the result found in 'closed' isn't the specified issue, but another one which probably references it).

What is the current bug behavior?

When I try this kind of search no result is found.

What is the expected correct behavior?

When I search for a given issue, I should be able to find the specific issue.

Output of checks

This bug happens on GitLab.com, but also on my local installation (GitLab Community Edition 9.0.5)