Currently, the xmlns and schemaLocation attributes have a trailing "/graphml" appended. This appears to be unnecessary (see http://graphml.graphdrawing.org/primer/graphml-primer.html#Header) and causes conflicts with third-party readers such as networkx.
Issue is present in latest repo. A patch is attached.
P.S. I don't have a bitbucket account, but you can email at thaines_at_astro.wisc.edu if you have any questions.