Okay, at -r85630 on branches/py3k, I ran:

./python.exe -m test.regrtest -uall -F test_urllibnet

And after 158 retries, got the same error I had before:

test test_urllibnet failed -- Traceback (most recent call last):
  File "/Users/pythonbuildbot/test/build/Lib/urllib/request.py", line 1504, in open
    return getattr(self, name)(url)
  File "/Users/pythonbuildbot/test/build/Lib/urllib/request.py", line 1676, in open_http
    return self._open_generic_http(http.client.HTTPConnection, url, data)
  File "/Users/pythonbuildbot/test/build/Lib/urllib/request.py", line 1659, in _open_generic_http
    response = http_conn.getresponse()
  File "/Users/pythonbuildbot/test/build/Lib/http/client.py", line 1027, in getresponse
    response.begin()
  File "/Users/pythonbuildbot/test/build/Lib/http/client.py", line 347, in begin
    version, status, reason = self._read_status()
  File "/Users/pythonbuildbot/test/build/Lib/http/client.py", line 303, in _read_status
    line = str(self.fp.readline(), "iso-8859-1")
  File "/Users/pythonbuildbot/test/build/Lib/socket.py", line 267, in readinto
    return self._sock.recv_into(b)
socket.error: [Errno 9] Bad file descriptor