Branch-name for pull requests

I’m using buildkite to build pull-requests but I’m confused about one behaviour I see: When I first submit a PR the request name is:

buildkite/[pipeline-slug]

but if it fails and I restart the build it appears as:

buildkite/[pipeline-slug]/pr

How do I get a consistent behaviour so I can properly set the branch requirements in github?

Example PR -> https://github.com/thirtytwobits/nanaimo/pull/14
Pipeline (public) -> https://buildkite.com/friends-of-scott/nanaimo-pr

Thanks.