See this - I did this manually on one of our test servers: 
GET / HTTP/1.0

HTTP/1.1 400 Bad Request
Date: Thu, 20 Nov 2003 09:30:34 GMT
Server: Apache/1.3.26 (Unix) mod_gzip/1.3.19.1a
Connection: close
Content-Type: text/html; charset=iso-8859-1

[download]
The request was input manually. The request is HTTP 1.0, but Apache returns HTTP/1.1. The same behaviour was shown by IIS on another machine we have here.

In reply to I think Liz is right by l3nz
in thread LWP::UserAgent Wrongly Uses HTTP/1.1 by Anonymous Monk

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