Googlebot makes HTTP/1.0 requests without host header?

At least, that's almost all I have in my access log for more than 2
months now. Which, I believe, is a problem. My domain is virtual, and
the webhost returns an eternal "Coming Soon" page on those requests.
So, if I'm reading the signs right, I get an almost daily hit on
robots.txt, hit on the google sitemap, and bye. It's not spidering or
indexing anything, and it even dropped my frontpage from the cache, it
seems, where it was some time ago.

Now, my site may be low quality according to their standards, but
that's not for Google to decide before their bot has even had a look at
it. And, thank God, there's Microsoft Search to flatter our egos when
Google once again treats us with spite, so this is not supposed to be
the usual rant. Rather, I would like to know whether anyone sees a
connection between a Google Sitemap and the site being looked at with
http/1.0 requests, and whether it might be better to unregister that
sitemap on a virtual domain?