Dmitry Bufistov
It strikes to me now that the matter is not so subtle at all, since add_vertex() with vecS is very likely to invalidate vertex_iterators (clearly contrary to the documentation). In my case the issue was a bit obscured since it is not perfectly clear that source(edge_descriptor) and target(edge_descriptor) use vertex_iterators. I had expected that edge_descriptor stores two vertex_descriptors.
The problem is not with edge_descriptor it is in the operator++() of the edge_iterator class.
I think that edge_iterators are not directly affected, and its still save to use them to access, e.g., edge properties. Its also save to use operator++(). The problem is that calling source(...) on an edge descriptor dereferences a vertex_iterator, and THAT one may have been invalidated. Is that right? Regards, Julius