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I've posted something similar about this a month or so ago.
AltaVista appeared to be using an experimental crawler at the time which had limited support for referers and cookies, albeit referring page *within* my site. I emailed the contact addy and got no reply, which isn't a big surprise.
I don't think I've seen it since - but then again I'm not paying them :)
From my point of view I think referer was less surprising than the fact they seemed to be coping with a session cookie which was pretty impressive since no other commercial SE crawlers do this to my knowledge.