ejabberd_xmlrpc issue when executing mod_muc_admin: get_room_affiliations()

Hello,

I'm running Ejabberd 2.1.3 and one issue I have at the moment is when I try to execute one particular "mod_muc_admin:get_room_affiliations()" operation via ejabberd_xmlrpc - pretty much all of my other operation cmds work except that one.

If I run the command via ejabberdctl, no problem at all and naturally the same with mod_rest.

Note that mod_muc_admin:get_room_occupants() runs fine via ejabberd_xmlrpc.

% erl -pa '/usr/lib/ejabberd/ebin/'
Erlang R13B03 (erts-5.7.4) [source] [64-bit] [smp:8:8] [rq:8] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.7.4 (abort with ^G)
1> xmlrpc:call({127, 0, 0, 1}, 4560, "/", {call, get_room_occupants, [{struct, [{name, "blah"}, {service, "conference.mychatserver.com"}]}]}).
{ok,{response,[{struct,[{occupants,{array,[{struct,[{occupant,{array,[{struct,[{jid,"Bob@conference.mychatserver.com/Bob"}]},
{struct,[{nick,"Bob"}]},
{struct,[{role,"participant"}]}]}}]}]}}]}]}}
{ok,{response,[{struct,[{occupants,{array,[]}}]}]}}
2> xmlrpc:call({127, 0, 0, 1}, 4560, "/", {call, get_room_affiliations, [{struct, [{name, "blah"}, {service, "conference.mychatserver.com"}]}]}).
{error,"HTTP/1.1 500 Internal Server Error\r\n"}
3>

I did set extra logging and got this in ejabberd's log:

=INFO REPORT==== 2011-03-16 02:45:15 ===
D(<0.23353.6>:ejabberd_commands:314) : Executing command mod_muc_admin:get_room_affiliations with Args=["blah",
"conference.mychatserver.com"]

=ERROR REPORT==== 2011-03-16 02:45:15 ===
{xmlrpc_http,153,
{ejabberd_xmlrpc,handler,
{'EXIT',
{function_clause,
[{lists,flatten,[owner]},
{ejabberd_xmlrpc,format_result,2},
{lists,map,2},
{lists,map,2},
{ejabberd_xmlrpc,format_result,2},
{lists,map,2},
{ejabberd_xmlrpc,format_result,2},
{ejabberd_xmlrpc,do_command,6}]}}}}

My Ejabberd's config file does NOT have XMLRPC authentication turned on for these tests:
...
{4560, ejabberd_xmlrpc, []},
...

Any idea?

Thanks in advance

--Franky