using .data() member of std::string doesn't work for small strings?

Why does the following program print garbage instead of hello? Interestingly, if I replace hello with hello how are you, then it prints hello how are you.

#include <string>
#include <iostream>

class Buffer
{
public:
    Buffer(std::string s):
        _raw(const_cast<char*>(s.data())),
        _buffer(std::move(s))
    {    
    }

    void Print()
    {
        std::cout << _raw;
    }

private:
    char* _raw;
    std::string _buffer;
};    

int main()
{   
    Buffer b("hello");
    b.Print();
}