I just updated today to version 1.600 following the security advisory, and started noticing an strange problem on some jobs.
It seems that there was a change between 1.599 and 1.600 that causes the JOB_NAME environment variable to be "shared" between jobs, when executing a job the variable JOB_NAME is not the one of the current job but from another one.
I also noticed that the PATH variable is getting set to values of different jobs.
After downgrading to version 1.599 the problem went away. There have been no changes in plugins, only on the jenkins version itself.
I saw this https://issues.jenkins-ci.org/browse/JENKINS-26755 on the changelog and I have a hunch it could be related.