[schlupa]

What happens some times is that changes in the compiler fixes issues that were not well defined in the specification, or were bugs in the implementation. Programs that used the feature wrongly or that were in fact buggy then break when compiled with the better specified feature. It's comparable to compiling a K&R conforming C program with C89 or C99 enforcing: it will reveal bugs that were none in K&R (type punning, uninitialized variable, prototype violations, etc.).