devops Static web app Release task does not create preview environment

I have an Azure Static webapp running and a pipeline building PR builds. In the release task you can state the production branch, and all other branches should be released as preview environments.

From helptext: "Production branch. When specified and Deployment Environment is empty, deployments from other branches will be preview environments"

YML

steps:
- task: AzureStaticWebApp@0
  displayName: 'Static Web App: '
  inputs:
    workingDirectory: '$(System.DefaultWorkingDirectory)/my-portal'
    app_location: /
    skip_app_build: true
    skip_api_build: false
    is_static_export: false
    verbose: true
    azure_static_web_apps_api_token: 'token'
    production_branch: develop

When running on branch refs/pull/1028/merge - the deployment still happens on production and a release environment is not created.

Is there a different way to configure this behaviour in Azure Devops, or does it simply not work?