Caused by changing ticket.user.

Offending code is [py lino_xl.lib.tickets.models.Ticket#on_worked]:

def on_worked(self, session):
    """This is automatically called when a work session has been created
    or modified.

    """
if dd.is_installed('votes'):
        self.set_auto_vote(session.user, VoteStates.invited)

    elif dd.is_installed('stars'):

        star = get_favourite(self, user=session.user)
        if star is None:
            Star = rt.modules.stars.Star
            star = Star(owner=self, user=session.user)
            star.save()
    self.touch()

Its called when the demo sessions are loaded.

Looking at [url stackoverflow.com/questions/3597762/how-does-djangos-orm-manage-to-fetch-foreign-objects-when-they-are-accessed] helps to understand why the _user_cache feild is being passed to the change_watcher. However still doesn't explaine why creating a Start pointing at the session.user is causing this.