Common reasons for bugs in release version not present in debug mode

Question

What are the typical reasons for bugs and abnormal program behavior that manifest themselves only in release compilation mode but which do not occur when in debug mode?

Answer 1

In .NET, even if you don't use conditional compilation like #if DEBUG, the compiler is still alot more liberal with optimisations in release mode than it is in debug mode, which can lead to release only bugs as well.