Recent builds of Hudson have introduced a regression in parameterized builds, which get executed concurrently when they should not.

Here is a simple test case to reproduce the issue with Hudson 1.346 (latest version as I speak). Note that the "Execute concurrent builds if necessary (beta)" feature is disabled (checkbox not ticked).

• Make sure the system is configured to have at least 2 executors.
• Create a new freestyle job 'Test'.
• Tick 'This build is parameterized' and add a 'Dummy' String parameter.
• Add an 'Execute shell' build step with the following script: 'export $WORKSPACE && sleep 30'.
• Save the job.
• Schedule 3 builds with different parameter values (a/b/c), quickly enough so that two builds get queued before the first one finishes.
• Wait for the first build to finish.
• Watch the 'Build history' frame: it will show two builds with a progress bar.
• Upon completion, one of the two builds executed concurrently will have the following console output, proving that both builds were executed at the same time (notice 'workspace@2'):

[workspace@2] $ /bin/sh -xe /tmp/hudson8995552964371253777.sh
+ echo /var/hudson/jobs/test/workspace@2
/var/hudson/jobs/test/workspace@2
+ sleep 20
Finished: SUCCESS

This issue may be related to JENKINS-2997 and JENKINS-5229. Note that JENKINS-2997 was a display-only issue and has been around for much longer.