What is the expected behavior of tellg() when std::stringstream is constructed with ("some content", std::ios::in|std::ios::ate)?

I have the following piece of code that surprised me (using libstdc++4.8)...

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int main() {
    std::string s("some content");
    std::stringstream ss(s, std::ios::in|std::ios::ate);
    std::istream& file = ss;
    //ss.clear(); Makes no difference...
    std::cout << "tellg() pos: " << file.tellg() << std::endl;
    return 0;
}

... which has the following output.

tellg() pos: 0

This behaviour is different to when using std::ifstream(std::ios::ate).

• Is this behaviour correct/expected?
• Does one need to explictly seekg(0, std::ios::end) despite opening with ate?
• clearing the state doesn't make a difference.
• Please note that the string has content.