schroedinbug

schroedinbug: /shroh'din-buhg/ n.  [MIT from the
   Schroedinger's Cat thought-experiment in quantum physics] A design
   or implementation bug in a program that doesn't manifest until
   someone reading source or using the program in an unusual way
   notices that it never should have worked, at which point the
   program promptly stops working for everybody until fixed.  Though
   (like {bit rot}) this sounds impossible, it happens; some
   programs have harbored latent schroedinbugs for years.  Compare
   {heisenbug}, {Bohr bug}, {mandelbug}.