Class operator[] does not return a lhv

Consider this class:

#include <vector>
using namespace std;

template<typename T>
class Vector{
private:
    size_t      size_;
    vector<T>   items;

public:
    Vector(){ size_ = 0; }
    inline void clear(){ size_ = 0; }
    inline void push_back( const T item ){
        if( items.size() == size_ )
            items.push_back( item );
        else
            items[size_] = item;
        size_++;
    }
    inline const T& operator[](int i) const { return items[i]; }
    inline T& operator[](int i) { return items[i]; }
};

int main(int argc, char *argv[]){
    Vector<bool> vec;
    vec.push_back( true );
    if( vec[0] )
        vec[0] = false;
}

When compiling with MSVS 2013 you get the following error for the non const operator[]: error C2440: 'return' : cannot convert from 'std::_Vb_reference<std::_Wrap_alloc<std::allocator<char32_t>>>' to 'bool &'

Changing the return statement in return (T&)(items[i]); results in a warning warning C4238: nonstandard extension used : class rvalue used as lvalue

The program runs (in debug mode) but the last statement does not change the value of vec[0] (as you should expect for a rhv).

What's wrong here?