There's also some weird double personality issues going on with their compilers in MSVC2013, for example they support designated initializers in plain C but not in C++. So you get partial C99 inside pure C or C89 (MS flavored) under C++.
I forgot where I read the quote, but for a decade Microsoft saw the plain C compiler as tool exclusively meant for Windows development. While gcc and later clang adopted and embraced new C idioms, like the struct syntax I mention, they kept their plain C support frozen in time.
I also found weird behavior in MSVC when pushing the C preprocessor VERY hard (nested variadic macros. That would require an entire blog post for itself...)
