ansible-pull only does "git pull" on first run, then uses same revision forever

I’m finding that the first ansible-pull run works perfect, but if I run it again after the initial run to get updates it continues to use the same revision. I’m working around it by using the --purge flag, but I think that means a full clone every time instead of just a pull. I’m invoking it like so: “/usr/local/bin/ansible-pull --purge --extra-vars=‘some_vars=“some values”’ -U https://git-codecommit.us-east-1.amazonaws.com/v1/repos/blah ‘dir/node-role.yml’”

Is this expected? Should I be filing a bug?

Versions:
ansible-pull: 2.1.0.0

python: 2.7.10
Amazon Linux