I agree with you. I'm sure the browser doesn't make stuff up... ;)
Error logging works. I tried that by adding faulty stuff to the script and the stuff really shows up within the log.
I somehow get the feeling it's got to do something with the interaction prototype<->perl script. If i run the perl script directly off the command line with the several POST arguments as cl-arguments, i get no errors at all. It always shows the expected behaviour.
Has anybody of you ever worked with prototype and perl and knows where this error could come from?