RapidXML / C++ - parsing into a static class member

Question

I have a class with a rapidxml::xml_document, but when I try to parse XML into it, it populates with... well, not garbage, but information about my namespaces and the like.

In the code below I have examples of what I've tried, commented out, and a local variable, doc being properly populated from the class member string.

Any ideas?

.h

class PrintHeadGeometry
{
    // XML Stuff
    static rapidxml::xml_document<> m_xmlDocDPHX;   
    static std::string m_xmlStringDPHX;  

    // etc
};

.cpp

// near the top
rapidxml::xml_document<> PrintHeadGeometry::m_xmlDocDPHX;
std::string PrintHeadGeometry::m_xmlStringDPHX = "";

// in my "load" function
std::ifstream file(filename);
std::stringstream buffer;
buffer << file.rdbuf();
file.close();
std::string content(buffer.str());
m_xmlStringDPHX = content;

// NEITHER OF THESE WORK - I WANTED THE TOP ONE, IDEALLY
//
//m_xmlDocDPHX.parse<0>(&m_xmlStringDPHX[0]);
//m_xmlDocDPHX.parse<0>(&content[0]);

// THIS WORKS THOUGH
//
rapidxml::xml_document<> doc;
doc.parse<0>(&m_xmlStringDPHX[0]);