XF 2.2 use the prefix_macro, set selected

[Robert9]

                <xf:formrow label="{{ phrase('prefix') }}" rowtype="input">
                    <xf:js src="xf/prefix_menu.js" min="1" />
                    <xf:macro template="public:prefix_macros" name="select"
                              arg-type="thread"
                              arg-selected="{$thread.prefix_id}"
                              arg-prefixes="{$threadPrefixes}"
                              arg-name="prefix_id"
                              arg-href="{{ link('forums/prefixes') }}"
                              arg-listenTo="#js-threadNodeList" />
                </xf:formrow>

{$thread.prefix_id} exists.
The select is shown.
But my prefix is not selected.

I try do find examples in other addons, but everywhere this syntax is used.
What can i do now, please?