Well, there are no way to realize that let first job keep active.
But with some notify scripts an techniques, we can track stuck jobs.
For detail, see System Administrator's Guide vol II, page 167.
NetBackup 5.1 System Administrator's Guide Volume II
http://support.veritas.com/docs/268091
And, just for canceling stack jobs, get active job IDs with "bpdbjobs -report", and cancel them with "bpdbjobs -cancel job_id1,job_id2" at a time.