[boost] [graph] adjacency_list::operator=()

Hello all, If I have an adjacency_list g and I call g = g; all of the vertices and edges of g are removed. This is not what I would expect; I would expect that this operation would not change g. 1. Is this the desired behavior? (It seems different than what other types do.) 2. Is this issue old news? (I couldn't find it on the mailing list archives but it may well be there.) Thanks, David