This reminds me of a time a friend was doing a K&R C homework assignment using the campus computer lab and the computer kept giving an integer result for float values. It turns out the 486 had a defective FPU. Windows 95 ran fine and everything. It sat among a dozen identical stations unnoticed.

Imagine loosing your mind trying to figure out what you're doing wrong, only to discover your computer is bad at math.

Since then I have found countless "unbelievable" situations where technology behaved out of character.