It can get even more "fun" with Java. Your code can start running through an interpreter, then after a while suddenly be transformed by a JIT engine. The interpreter and the JIT engines (there's more than one JIT engine) have different bugs. The optimizations made by the JIT engine can depend on the data which went through your method before the JVM decided to optimize it.

I'm not finding it right now, but I recall seeing a few weeks ago a presentation with several of these sorts of bugs in a recent version of Java (all reported and fixed): after a number of iterations, it suddenly starts returning wrong results.