"Fast forward not possible" message includes non-rendering HTML tag

This is a minor issue that appears on GitLab.com, which seems likely to also affect GitLab Community Edition.

When a fast-forward merge is not possible (due to other changes that have happened on the master branch since the merge request was opened), the following message appears:

Fast-forward merge is not possible. Rebase the source branch onto <span class="label-branch">master</span> to allow this merge request to be merged.

However, the HTML tag (<span class="label-branch">) does not render, possibly due to escaping or use of .textContent instead of .innerHTML. I did a quick search through the code but couldn't find where this message came from.

Here's what it looks like: