Source : Free On-Line Dictionary of Computing

ill-behaved
     
        1. [numerical analysis] Said of an {algorithm} or
        computational method that tends to blow up because of
        accumulated roundoff error or poor convergence properties.
     
        2. Software that bypasses the defined {operating system}
        interfaces to do things (like screen, keyboard, and disk I/O)
        itself, often in a way that depends on the hardware of the
        machine it is running on or which is nonportable or
        incompatible with other pieces of software.
     
        In the {IBM PC}/{mess-dos} world, there is a folk theorem
        (nearly true) to the effect that (owing to gross inadequacies
        and performance penalties in the OS interface) all interesting
        applications are ill-behaved.
     
        See also {bare metal}. Opposite: {well-behaved}, compare
        {PC-ism}.
     
        [{Jargon File}]