operator<< called only in Linux

Question

I'm using easyloggingpp in a "big" cross platform project. Big enough that I can't create a simple running example that reproduce the behavior I'm about to describe.

So I have some enum type define in some header, let say:

In types.h:

typedef enum MyEnum
{
    First,
    Second
} MyEnum;

The enum is a C enum since the project is ABI safe and the API is a thin layer of C functions and types (Our implementation for the Hour Glass pattern)

and it also has 2 functions to handle printing, assume that these are the functions (in reality only the functions' bodies are different):

inline std::ostream & operator << (std::ostream & out, MyEnum value) 
{ 
    return out << get_string(value);
} 

In types.cpp, I have:

namespace MyNamespace
{
    const char* get_string(MyEnum value)
    {
        assert(0);
    }
}

If I call something like this in my code

MyEnum x = First;
std::stringstream os;
os << "Value of x is: " << x;

The assert(0) I have in the get_string() function will be triggered.

But if I call the logger:

LOG_INFO("Value of x is: " << x);

For some reason, In Visual Studio (2017 if that matters), when the logger's inner stream member (which is also of type std::stringstream) is called with x it calls the <ostream> function: _Myt& __CLR_OR_THIS_CALL operator<<(int _Val) , i.e. it treats the enum to an integer, and prints the value as a number instead of using my operator overload.

But, in Linux - the same code, compiled with gcc 5.4.0, calls my operator<< and does trigger the assertion.

I'm not really sure where to start in order to understand this...

So the real question is - what could cause such a difference between compilers\OSs? and where do I start with debugging it? or if someone knows what is causing this, I'd love to know.

EDIT:

LOG_INFO is a macro of the logging infrastructure which eventually calls: m_logger->stream() << msg; where m_logger->stream() returns std::stringstream& and msg is a templated value parameter which in my example is the instance of x