Boost: access graph specific properties with read_graphml()

I am trying to read graph related (custom) properties from a .graphml file created with yEd using the Boost Graph library. Reading vertex and edge (dynamic_)properties works but my graph properties are always empty. I've also came across how to read graph-domain attributes with boost::read_graphml? but that solution just produces empty strings (it's in the code below). Apart from that, I was not able to find much information about the problem.

Here's the shortened code (complete working example test.cpp here):

struct VertexProperties { string url, description; };
struct EdgeProperties { string url, description; };
struct GraphProperties { string title; };
// ...
typedef adjacency_list<vecS, vecS, directedS, VertexProperties, EdgeProperties, GraphProperties> DirectedGraph;
typedef dynamic_properties Properties;
DirectedGraph graph(0);

Properties props(ignore_other_properties);
props.property("url", get(&VertexProperties::url, graph));
props.property("description", get(&VertexProperties::description, graph));
props.property("url", get(&EdgeProperties::url, graph));
props.property("description", get(&EdgeProperties::description, graph));
map<string, string> attribute_name2name;
associative_property_map<map<string, string>> graphname_map(attribute_name2name);
props.property("title", graphname_map);
// ...
read_graphml(validated, graph, props);
graph[graph_bundle].title = get(graphname_map, "title");
cout << "\"" << graph[graph_bundle].title << "\"" << endl;

You can compile the full code using g++ test.cpp --std=c++11 -o test -lboost_graph. Running it with ./test simple_graph.graphml produces just "" instead of "foobar" which is the expected output since the graph has the

<data key="d1"><![CDATA[foobar]]></data>

tag which is defined as

<key attr.name="title" attr.type="string" for="graph" id="d1">
  <default/>
</key>

I've uploaded an simple_graph.graphml example file (not enough rep. to post img / more details).

Minor follow-up question: is it possible to load the graph w/o 'fixing' the yEd-exported file (cf. code)? The parser always complains about lines like this (not sure if it's even permitted in the GraphML standard):

<key for="port" id="d2" yfiles.type="portgraphics"/>

with this error:

parse error: unrecognized type "" for key

Any help/ideas are highly appreciated. Thank you very much!