Comment 4 for bug 1039493

Okay, this is weird. I can reproduce your issue on almost the same config (Python 2.7.3 instead of 2.6.x) with the source code example you provided _only_ if I do not call igraph.Graph.__init__(self, directed=directed) in the constructor. If this call is not there, I get almost exactly the same valgrind output as you, with exactly the same stacktrace in the end. If this call is there, everything works fine.

Can you please attach a single, self-contained .py file that reproduces the problem on your machine?