In version 0.9.0 we have

(message.hpp - line 98)
string_type body() const {
return _body;
}

this does not work with
(linearize.hpp - line 140)
typename body_range::type body_data = body(request).range();
return boost::copy(body_data, oi);

.. since body(request) creates a new string_type,
the body_data range is invalid at the copy statement.

The easiest fix is to make the const body observer return a const reference.

(message.hpp - line 98)
string_type const& body() const {
return _body;
}

... may be an idea to do the same for source, destinarion and headers too.