read-resource shows a 'default-stack' that is not described

[standalone@localhost:9999 subsystem=jgroups] :read-resource
{
"outcome" => "success",
"result" => {
"default-stack" => "udp",
"stack" =>

{"udp" => undefined}

}
}
[standalone@localhost:9999 subsystem=jgroups] :read-resource

read-resource read-resource-description
[standalone@localhost:9999 subsystem=jgroups] :read-resource-description
{
"outcome" => "success",
"result" => {
"description" => "The configuration of the jgroups subsystem.",
"head-comment-allowed" => true,
"tail-comment-allowed" => true,
"namespace" => "urn:jboss:domain:jgroups:1.1",
"children" => {"stack" => {
"description" => "The configuration of a jgroups protocol stack.",
"min-occurs" => 1,
"max-occurs" => 2147483647,
"model-description" => {}
}}
}
}

One level deeper:

[standalone@localhost:9999 stack=udp] :read-resource
{
"outcome" => "success",
"result" => {
"protocols" => [
"PING",
"MERGE2",
"FD_SOCK",
"FD",
"VERIFY_SUSPECT",
"BARRIER",
"pbcast.NAKACK",
"UNICAST2",
"pbcast.STABLE",
"pbcast.GMS",
"UFC",
"MFC",
"FRAG2",
"pbcast.STATE_TRANSFER"
],
"protocol" =>

{ "PING" => undefined, "FD_SOCK" => undefined, "FD" => undefined, "VERIFY_SUSPECT" => undefined, "BARRIER" => undefined, "FRAG2" => undefined, "MERGE2" => undefined, "pbcast.GMS" => undefined, "pbcast.STATE_TRANSFER" => undefined, "UNICAST2" => undefined, "UFC" => undefined, "MFC" => undefined, "pbcast.NAKACK" => undefined, "pbcast.STABLE" => undefined }

,
"transport" =>

{"TRANSPORT" => undefined}

}
}
[standalone@localhost:9999 stack=udp] :read-resource

read-resource read-resource-description
[standalone@localhost:9999 stack=udp] :read-resource-description
{
"outcome" => "success",
"result" => {
"description" => "The configuration of a jgroups protocol stack.",
"children" => {
"transport" =>

{ "description" => "The configuration of a transport for a protocol stack.", "min-occurs" => 0, "max-occurs" => 1, "allowed" => ["TRANSPORT"], "model-description" => undefined }

,
"protocol" =>

{ "description" => "The configuration of a protocol within a protocol stack.", "min-occurs" => 0, "max-occurs" => 2147483647, "model-description" => undefined }

}
}
}