[Boost.Graph] graph.vertices property creates new objects

[George Sakkis]

I've just started toying with the python bindings of BGL and I'm 
puzzled from the following:

>>> from boost.graph import Graph
>>> g = Graph()
>>> v = g.add_vertex()
>>> g.vertices.next() == v
True
>>> g.vertices.next() is v
False

It seems that the vertices iterator creates new vertex objects every 
time instead of iterating over the existing ones. This essentially 
prevents, among other things, storing vertices as keys in a dictionary 
since the hashes of the stored and the new vertex differ although they 
compare equal. Is this really what's happening, and if so, why ?

George