* Optimizer bugs. Thankfully these are less common nowadays. It the "good old days" of new compilers this happened quite a bit. Embedded code: * Missing "vola

* Optimizer bugs. Thankfully these are less common nowadays. It the "good old days" of new compilers this happened quite a bit. Embedded code: * Missing "volatiles" which allow the optimizer to optimize out "unused" loads and stores to hardware or multitasking shared variables. * Race conditions (e.g. unsynchronized access to multitasking shared variables). Making the code run slower changes the access pattern, often times obscuring the bug.