If you don't see the debug messages, you may be suffering from buffering. This may be especially the case when the program terminates unexpectedly and the script is not able to flush its buffers.
in reply to Re^2: unexpected quit - no error message
in thread unexpected quit - no error message
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James