Move-construction can slice objects by SecurityException

I've spent some hours debugging an access violation. It turned out that a std::ifstream was sliced to a std::istream due to a typo in the code. I'm curious whether it is legal what happened to me, because the compiler first calls ifstream(ifstream&&) and then istream(istream&&), although the object is only returned once. Please see the code I provided.

#include <cassert>
#include <fstream>


std::ifstream OpenRead(const char* file) {
    std::ifstream stream(file, std::ios_base::in | std::ios_base::binary);
    if( !stream.good() )
        throw "Unable to open file!";

    stream.exceptions(std::ios_base::badbit);
    return stream;
}


int main() {
    static const char* filename = "main.cpp";

    std::istream input = OpenRead(filename);        // access violation
    //std::ifstream input = OpenRead(filename);        // fixes the bug
    char test = input.get();
    assert( test == '#' );
}