If cloning from a mirror with a pull request trigger event, updates to the source branch will not trigger a job to build. The job configuration will only subscribe to mirror synchronized events, which are discarded because webhooks aren't pull request events.

I've also noticed that when changing the job to clone from upstream instead of from a mirror, we do not update our subscriptions, meaning the job will continue to ignore triggers. This needs more investigation but potentially is a separate issue.

Steps to reproduce:

• Create a multibranch pipeline job against a new repository (without a Jenkins webhook) with a pull request trigger and a mirror clone URL
• Open a pull request and verify the PR is being opened correctly
• Make a push to the source branch

Expected:

The job is triggered, and builds the correct commit

Actual:

The webhook is ignored by the job and no commit is created.

Workaround:

There is no workaround for this behaviour.