If I push to source control in Stash and the hook notifies jenkins to build a job, it correctly shows the change log of only the commits since the last build. If i ever trigger the build manually from jenkins UI, the change log will show every change I have made since the last manual build (days, weeks or months worth of commits)

Able to reproduce in many older version combos of jenkins/git as well like 1.592 and 2.2.2

Talked with Mark Waite about this briefly at JUC on 9/2 and it is believed to be a bug.