There appears to be an issue with the "Use Upstream Project revision" option in the perforce plugin.
When we set that field to the name of the upstream job then Jenkins is not using changeset from the latest successful build from that job, but the changeset from the previous build.

I wonder if this is some issue with the job being directly upstream from the one where the "Use Upstream Project revision" is set and being built immediately afterwards.

What is the mechanism that the perforce plugin uses to communicate the changeset numbers between jobs?
I have looked at the changelog.xml in the builds directory but that seems to be correct.