Changes to server-config not persisted

Heiko Braun reports that the following changes update in-memory state, but are not persisted back to host.xml:

{
"operation" => "composite",
"address" => [],
"steps" => [

{ "operation" => "write-attribute", "address" => [ ("host" => "local"), ("server-config" => "server-one") ], "name" => "socket-binding-group", "value" => "standard-sockets" }

,

{ "operation" => "write-attribute", "address" => [ ("host" => "local"), ("server-config" => "server-one") ], "name" => "socket-binding-port-offset", "value" => 90 }

]
}

The in-memory state and host.xml state can be seen:

[localhost:9999 /] /host=local/server-config=server-one:read-resource
{
"outcome" => "success",
"result" => {
"path" => undefined,
"system-property" => undefined,
"interface" => undefined,
"jvm" =>

{"default" => undefined}

,
"socket-binding-group" => "standard-sockets",
"socket-binding-port-offset" => 90,
"name" => "server-one",
"group" => "main-server-group",
"auto-start" => true
},
"compensating-operation" => undefined
}

<server name="server-one" group="main-server-group" auto-start="true">
<jvm name="default"/>
</server>