This trick is VERY often used as a guarantee that the client will pay. Many custom projects and expensive machines have this (Although NO ONE will admit it). Most equipment especially custom stuff is sold or developed on credit or depsoit. At the end of a job if someone refuses to pay their bill, for whatever reason they might find that thier equipment falls over. So they ring the tech - "I'm sorry we can't repair that equipment as we..."

Quite often if the customer pays with no problems these features are disabled in a 'routine follow up test of the equipment'

By the way I only find the time every couple of days to check out these topics. J, how do you find so much time?