Bitbucket Server integration plugin set to trigger on Pull Request events only is supposed to run builds for branches for which specific PR event applies. However, it builds all the new commits for all the branches, not only for those with PR opened.

Let's consider a situation:

1. A build plan in Jenkins using Bitbucket Server integration plugin set to trigger on Pull Request events only
2. We have 4 branches in a repo: master, FEAT-1, FEAT-2, FEAT-3.
3. We have one open PR: FEAT-3 -> master.
4. We push a new commit to FEAT-1 - the build doesn't start
5. We push a new commit to FEAT-2 - the build doesn't start
6. We push a new commit to FEAT-3 - the build starts first for FEAT-1, then FEAT-2, and after that starts for FEAT-3
   All the builds happen for the head commits of each branch.

Tested on:
Bitbucket 7.15
Bitbucket Server Integration 3.1