Bad behaviour with upvotes and / or downvotes in a Merge Request

Summary

When the same user make multiple upvotes on a Merge Request, he is added multiple times. I think that each user should have only one vote.

Steps to reproduce

• Click multiple times on upvote in a Merge Request and check the title.
• OR click upvote and downvote.

Expected behavior

The user should be added one time only in the title. And the same user shouldn't be able to upvote and downvote the same MR...

Relevant logs and/or screenshots

<div class="award active" title="" data-original-title="me, me, me, me, me, me">
<div class="icon emoji-icon emoji-1F44D" title="thumbsup" data-aliases="" data-emoji="thumbsup" data-unicode-name="1F44D"></div>
<div class="counter">1</div>
</div>

Title changed from Problem with upvote or downvote in a Merge Request to Bad behaviour with upvotes and / or downvotes in a Merge Request

mentioned in merge request !2804 (merged)

mentioned in issue #13374 (closed)

mentioned in commit 7ffcc5a1

Status changed to closed by merge request !2804 (merged)

mentioned in commit e654e68c

Hello,

we are using GitLab Community Edition 9.1.4 (fed799ae) and we manage to reproduce the bug. A coworker get to reward 3 thumbs up on a MR (see screenshot)

And also here.