It is because the tPrejob_1Process() method and the tJava_1Process() are called separately in the runJobInTOS() method.
They are in two try-catch-finally blocks.
The solution is to select the "Exit JVM immediately" option in tDie->Advanced Settings.
For me it doesn't work because i want to execute the tPostJob even tDie quit tPreJob.
The only solution i found is to put a component (tWarn or tJava) starting the job an linking it to the real start with an if link (condition : no error message, for example)