Build flow plugin parallel builds are not parallel

[Mike Finneran]

When I execute the following build flow script on a cluster of four 
identical nodes, only one node is used to execute all twelve instances of 
"job-Build".
If I pull that node, All instances are still build on only one node, just 
the next node that is still on line.
I would have thought that all four nodes would be used to execute the 
"Job-Build" instances four at a time in parallel.
Am I doing something wrong in the code?
Also, I'm using the latest jenkins (build 1.492) and the latest build flow 
plugin (build 0.6) 

build("Job-Init");
parallel (
    { build("Job-Build", JOB_NUMBER: "1") },
    { build("Job-Build", JOB_NUMBER: "2") },
    { build("Job-Build", JOB_NUMBER: "3") },
    { build("Job-Build", JOB_NUMBER: "4") },
    { build("Job-Build", JOB_NUMBER: "5") },
    { build("Job-Build", JOB_NUMBER: "6") },
    { build("Job-Build", JOB_NUMBER: "7") },
    { build("Job-Build", JOB_NUMBER: "8") },
    { build("Job-Build", JOB_NUMBER: "9") },
    { build("Job-Build", JOB_NUMBER: "10") },
    { build("Job-Build", JOB_NUMBER: "11") },
    { build("Job-Build", JOB_NUMBER: "12") },
)
build("Job-report");