Astonishing C++ streams

Let's talk about about C++, as it deserves it from time to time.
Especially because I've lost a couple of days on a not-enough-advertised-feature:

    std::ifstream in;
    in.open("somefile",std::ifstream::out);


 (https://www.destroyallsoftware.com/talks/wat)

Opening an input file stream for output is not at all convoluted.
It's both a crystal clear code and a brilliant idea! 
Good enough to transcribe it in the standard library:

http://www.cplusplus.com/reference/fstream/ifstream/open/


What difference does it make with fstream? Or should I rather open an ofstream for input? It leaves plenty of room for speculation. if someone knows, he shall write a blog post immediately!
But if the standard offers some weird path, by virtue of Murphy's law, be sure that someone will follow it, whether accidentally or not.

Murphy's law has more to offer: Microsoft implementation changed somewhere between .NET 2003 and .NET 2010, so that opening an input file stream for output on a write-protected file does now fail, what it didn't previously...
Of course, the file has to be read only at deployment site, not in developer's configuration where we have debuggers, otherwise things would be much too trivial.

Recompiling a legacy application while not exerting enough code review is a dangerous thing, so let's not blame C++ for our own mistakes. Except that C++ did not especially help here.

My colleagues said: "tu-mourras-moins-bete" (auf deutsch). Not so sure: I feel like this kind of information is not going to reduce the entropy in my brain.
 
I'm not going to change C++. I can't. But I'm itching to simplify our own Squeak Stream hierarchy with such reduction of entropy in mind. Don't push me!