For jobs that receive pull request events, and are cloning from a mirror rather than an upstream, the following scenario could occur:

• A ref change is made to an open pull request
• Bitbucket fires a Source branch updated event
• Jenkins receives that event, containing new commits and a head event is fired
• The mirror job attempts to clone from the unsynced mirror, receiving and build stale commits
• Bitbucket later fires a mirror sync event, which is unanswered

This behaviour has not yet been replicated and should be explored as part of addressing if this is an issue.