My quick guess is the lock's "info" file is empty somehow (which isn't supposed to happen). bzr probably should handle this situation more gracefully somehow... probably a conservative approach would be telling the user something strange has happened to the lock, and please use break-lock to clear it. (And probably involves fixing the lock breaking code to handle a corrupt/empty info file too).
My quick guess is the lock's "info" file is empty somehow (which isn't supposed to happen). bzr probably should handle this situation more gracefully somehow... probably a conservative approach would be telling the user something strange has happened to the lock, and please use break-lock to clear it. (And probably involves fixing the lock breaking code to handle a corrupt/empty info file too).