Merging a pull request marks the merge commit as public, although repo is not a publishing one

We use Mercurial with the evolve extension (lab feature) enabled. Also, our repo is set to be non-publishing. This means pushed commits stay in phase "draft".

This does not work for PR merges. When a PR is merged in the BitBucket UI, both the close-branch and the merge commit have phase "public".

What I expect: The commits should be in phase "draft" because our repo is set to be non-publishing.