Autobuild for tags on a branch other than master

I have a fork of a GitHub repository. In that GitHub repository I have a branch. I then opened a pull request to contribute the feature on the branch of the fork back to the parent project.

Since others are reviewing the PR and may want to try out the PR build, I have enabled autobuild for the fork in that repository. Additionally, I added a Branch source type to build the branch holding my PR. This is working properly.

However, I also want to use tags on that branch to refer to the version of the source I am currently using. I want a Docker image tagged with this version. Unfortunately, this does not work. I believe it is not working because the tag is on the branch and does not appear on master. The build status shows EMPTY.

Is this expected behavior? Is there any way I can have Docker Hub build tags on a branch other than master? It seems like it would be a common scenario when a project is using a branch for a release and tagging bug fixes on that branch.

Thank you.