Comment 2 for bug 715000

Trying with lp:ubuntu/lucid/ssss I see

471 known_graph = self.repository.get_known_graph_ancestry(
472 [last_revision])

which internally fails to find last_revision in either of the _fallback_vfs that it checks.

I suspect this bug occurs when the tip revision is in a stacked-on repository. It may
happen when any revision in the history is stored in a stacked-on repo, I'm not
sure yet.

Thanks,

James