green lightning

green lightning n.  [IBM] 1. Apparently random flashing
   streaks on the face of 3278-9 terminals while a new symbol set is
   being downloaded.  This hardware bug was left deliberately unfixed,
   as some genius within IBM suggested it would let the user know that
   `something is happening'.  That, it certainly does.  Later
   microprocessor-driven IBM color graphics displays were actually
   *programmed* to produce green lightning!  2. [proposed] Any
   bug perverted into an alleged feature by adroit rationalization or
   marketing.  "Motorola calls the CISC cruft in the 88000
   architecture `compatibility logic', but I call it green
   lightning".  See also {feature} (sense 6).