Odd behaviour: multiple builds per commit

I have a private repo in an organisation (fnproject) that when I push commits to causes two builds to be triggered rather than one; this is not something I’ve set up and has just started happening, I only want a single build per commit (why have a redundant build?)

For anyone at circle, the repo in question is fnproject/fn-java-fdk and an example branch demonstrating multiple build behaviour is ci/persist-integration-test-artifacts