提升序列化版本不好

Question

使用版本1.49.0的boost序列化版本运行时，以下代码会破坏版本号。

#include <boost/serialization/nvp.hpp>
#include <boost/archive/xml_oarchive.hpp>
#include <iostream>

using namespace std;
using namespace boost::archive;

class Nested {
public:
    explicit Nested()
    : mC()
    { }

    explicit Nested(char c)
    : mC(c)
    { }

private:
    friend class boost::serialization::access;

    template<class Archive>
    void serialize(Archive& ar, const unsigned int)
    {
        using boost::serialization::make_nvp;
        ar & make_nvp("c", mC);
    };

private:
    char mC;
};

BOOST_CLASS_VERSION(Nested, 0);

int main()
{
    Nested n('c');

    {
        using boost::serialization::make_nvp;
        xml_oarchive ar(cout);
        ar << make_nvp("Nested", n);
    }

    return 0;
}

使用版本1.49.0输出：

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<!DOCTYPE boost_serialization>
<boost_serialization signature="serialization::archive" version="9">
<Nested class_id="0" tracking_level="0" version="2057815296">
        <c>99</c>
</Nested>
</boost_serialization>

当我使用旧版本运行时，我会按预期获得0版本：

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<!DOCTYPE boost_serialization>
<boost_serialization signature="serialization::archive" version="6">
<Nested class_id="0" tracking_level="0" version="0">
        <c>99</c>
</Nested>
</boost_serialization>

我是否遗漏了不同版本的内容？还有其他人经历过这个吗？