Manual actions don't work as the only step in the pipeline

Admittedly, this is a different use case from the one described in the release announcement for GitLab 8.10, but I tried making a .gitlab-ci.yml file where there's a manual action as the only stage in a pipeline, and it didn't seem to cause any build or pipeline to appear in the UI at all, so there was nothing for me to click on to activate the manual action.

The .gitlab-ci.yml file looks something like this:

nightly_build:
    stage: build
    only:
        - branches
    when: manual
    script:
        - ...
    artifacts:
        expire_in: ...
        paths:
            - ...

release_build:
    stage: build
    only:
        - tags
    script:
        - ...
    artifacts:
        expire_in: ...
        paths:
            - ...

deployment1:
    stage: deploy
    dependencies:
        - release_build
    only:
        - tags
    script:
        - ...

deployment2:
    stage: deploy
    only:
        - tags
    dependencies:
        - release_build
    script:
        - ...