Can't set "append" attribute on file handlers

I can't tell what is really happening here. It seems to parse the "append" attribute OK, but it doesn't show up in the CLI. I've also set it programmatically in the console code, but I never get a value back for it.

<periodic-rotating-file-handler name="FILE">
<level name="INFO"/>
<formatter>
<pattern-formatter pattern="%d

{HH:mm:ss,SSS}

%-5p [%c] (%t) %s%E%n"/>
</formatter>
<file relative-to="jboss.server.log.dir" path="server.log"/>
<suffix value=".yyyy-MM-dd"/>
<append value="true"/>
</periodic-rotating-file-handler>

[standalone@localhost:9999 /] /subsystem=logging/periodic-rotating-file-handler=FILE:read-resource
{
"outcome" => "success",
"result" => {
"autoflush" => true,
"encoding" => undefined,
"file" =>

{ "path" => "server.log", "relative-to" => "jboss.server.log.dir" }

,
"formatter" => "%d

{HH:mm:ss,SSS}

%-5p [%c] (%t) %s%E%n",
"level" => "INFO",
"suffix" => ".yyyy-MM-dd"
}
}