Description of problem:
API script that logs in to Satellite through an RHN Proxy returns errors.After successful authentication, the system.custominfo.listAllKeys method is called, but it returns 0-length content ("header: Content-Length: 0"). This causes the connection to error out with "xml.parsers.expat.ExpatError: no element found: line 1, column 0". No errors found in Satellite-side logs. 
Version-Release number of selected component (if applicable):

# cat api-2036900.py 
#!/usr/bin/python

import xmlrpclib
sat = xmlrpclib.Server('http://rhn-proxy-fqdn/rpc/api', verbose=1)
key = sat.auth.login('xxxxx', 'xxxxx')
allkeys = sat.system.custominfo.listAllKeys(key)
for a in allkeys:
        print "%s" % (a['id'])

[root@dhcp242-204 ~]# python api-2036900.py 
connect: (xxxxxxxx, 80)
send: 'POST /rpc/api HTTP/1.0\r\nHost: dhcp242-204\r\nUser-Agent: xmlrpclib.py/1.0.1 (by www.pythonware.com)\r\nContent-Type: text/xml\r\nContent-Length: 215\r\n\r\n'
send: "<?xml version='1.0'?>\n<methodCall>\n<methodName>auth.login</methodName>\n<params>\n<param>\n<value><string>admin</string></value>\n</param>\n<param>\n<value><string>redhat</string></value>\n</param>\n</params>\n</methodCall>\n"
reply: 'HTTP/1.1 200 OK\r\n'
header: Date: Fri, 30 Jul 2010 10:50:41 GMT
header: Server: Apache/2.2.3 (Red Hat)
header: set-cookie: JSESSIONID=BD903724E89393575B84E2DA387DA8DD; Path=/rhn; Secure
header: content-length: 174
header: content-type: text/xml
header: Connection: close
body: '<?xml version="1.0" encoding="UTF-8"?><methodResponse><params><param><value><string>121278xc423ff8b1318e0eec790676e406eb437</string></value></param></params></methodResponse>'
connect: (xxxxxxxx, 80)
send: 'POST /rpc/api HTTP/1.0\r\nHost: dhcp242-204\r\nUser-Agent: xmlrpclib.py/1.0.1 (by www.pythonware.com)\r\nContent-Type: text/xml\r\nContent-Length: 212\r\n\r\n'
send: "<?xml version='1.0'?>\n<methodCall>\n<methodName>system.custominfo.listAllKeys</methodName>\n<params>\n<param>\n<value><string>121278xc423ff8b1318e0eec790676e406eb437</string></value>\n</param>\n</params>\n</methodCall>\n"
reply: 'HTTP/1.1 200 OK\r\n'
header: Date: Fri, 30 Jul 2010 10:50:41 GMT
header: Server: Apache/2.2.3 (Red Hat)
header: set-cookie: JSESSIONID=ADB3126AA19053C25F4671F35A59D733; Path=/rhn; Secure
header: transfer-encoding: chunked
header: content-type: text/xml
header: Content-Length: 0
header: Connection: close
Traceback (most recent call last):
  File "api-2036900.py", line 7, in ?
    allkeys = sat.system.custominfo.listAllKeys(key)
  File "/usr/lib/python2.4/xmlrpclib.py", line 1096, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.4/xmlrpclib.py", line 1383, in __request
    verbose=self.__verbose
  File "/usr/lib/python2.4/xmlrpclib.py", line 1147, in request
    return self._parse_response(h.getfile(), sock)
  File "/usr/lib/python2.4/xmlrpclib.py", line 1284, in _parse_response
    p.close()
  File "/usr/lib/python2.4/xmlrpclib.py", line 530, in close
    self._parser.Parse("", 1) # end of data
xml.parsers.expat.ExpatError: no element found: line 1, column 0

How reproducible:
Always

Steps to Reproduce:
1. Create Custom System Info Keys from the WebUI
2. Populate it.
3. Use the above API and let it go through a RHN Proxy Server
  
Actual results:
xml.parsers.expat.ExpatError: no element found: line 1, column 0

Expected results:
Should list all the Custom System Info Keys and it's contents

Additional info:
The same script does not encounter any errors when modified to log in directly to the Satellite.