Heisenbug and others
Heisenbug: A bug that disappears or alters its behavior when one attempts to probe or isolate it.
Bohr bug: A repeatable bug; Antonym of heisenbug.
Schroedinbug: 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.
Mandelbug: A bug whose underlying causes are so complex and obscure as to make its behavior appear chaotic or even non-deterministic.