build.author not resolving to expected username

[sjdrc]

I have the following pipeline:

  - name: notify
    image: plugins/slack
    settings:
      webhook:
        from_secret: slack_webhook_url
      link_names: true
      template: >
        {{#if build.pull }}
          *{{#success build.status}}✔{{ else }}✘{{/success}} {{ uppercasefirst build.status }}*: <https://URL/{{ repo.owner }}/{{ repo.name }}/pulls/{{ build.pull }}|Pull Request #{{ build.pull }}>
        {{else}}
          *{{#success build.status}}✔{{ else }}✘{{/success}} {{ uppercasefirst build.status }}: Build #{{ build.number }}* (type: `{{ build.event }}`)
        {{/if}}

        Commit: <https://URL/{{ repo.owner }}/{{ repo.name }}/commit/{{ build.commit }}|{{ truncate build.commit 8 }}>
        
        Branch: <https://URL/{{ repo.owner }}/{{ repo.name }}/commits/{{ build.branch }}|{{ build.branch }}>
        
        Author: <@{{ build.author }}>
        
        <{{ build.link }}|Visit build page ↗>

However, in slack the author of the PR is always mentioned, rather than the author of the most recent commit. Is this intended behaviour? The documentation states that it should be git author for current commit.