To reproduce:

• Create a set of external resources on a group of slaves, I use four slaves currently. Make sure that the 'Id' of the external resource is unique. Set a reasonable number of executors on each slave, I use ten on each. The four slaves should have a common label so that jobs are bound to any of those slaves.
• Create ONE job that requires an external resource by setting a 'Resource Selection Criteria', it should only be allowed to run on the common labelled group of slaves.
• Run the job several times in parallel, it works as expected. (My test-job prints out the value of ID and NET and then sleeps for 60 seconds.)
• Now create a FreeStyle/MultiJob/MultiConf/BuildFlow job and call the created job several times from the new job. Jobs will be stuck in the build-queue forever, because of "no available executors on the 'label-group'".

There is absolutely NOTHING in the log-files.