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It seems to me that you're indeed misusing it.
The correct way would be something like this (assuming response is a HTTPResponse object from httplib):
self.send_response(response.status)
for name, value in response.getheaders():
 self.send_header(name, value)
self.end_headers()
This is because send_response's second argument is the HTTP's "reason" field, i.e. invoking:
 self.send_response(123, 'FOOBAR')
results in 
 HTTP/1.1 123 FOOBAR\r\n
to be sent, followed by "Server" and "Date" headers. The second argument is not meant to be used for sending headers.
(When the second argument is omitted, a standard reason for the given status code is used.)