schroedinbug

/shroh'din-buhg/ [MIT: from the Schroedinger's Cat thought-experiment in quantum physics] n. 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.