jQuery Grid Plugin - jqGrid

I'm having a problem with collapsing in treeGrid by using the adjacency model.

I've tried severeal times to get it working but it seems i'm missing a point & the demo of jqgrid for the adjacency model isn't working as well.

The problem is - if i expand a column it works fine it loads the right data by xml & shows them.

But if i collapse the parent-column it does nothing. So the child-data is still shown and if i expand the parent

again it loads the data again and if have twice the children-elements.

I'm using jqGrid 3.6.4

js-code:

$(document).ready(
    function()
    {
        jQuery("#treegrid").jqGrid({
            treeGrid: true,
            treeGridModel: 'adjacency',
            treeModel: 'adjacency',
            url: xml_url,
            treedatatype: "xml",
            mtype: "POST",
            colNames:["id","name"],
            colModel:[
                {name:'id',index:'id', width:1,hidden:true,key:true},
                {name:'name',index:'name', width:180}
                 ],
            height:'auto',
            pager : jQuery("#ptreegrid"),
            ExpandColumn : 'name',
            caption: "Treegrid documents"
         });
    });

the xml of a child send by the server:

echo "<?xml version='1.0' encoding='utf-8' ? >";
    echo "<rows>";
    echo "<page>1</page>";
    echo "<total>1</total>";
    echo "<records>1</records>";
        echo "<row>";
        echo "<cell>" . $document->id ." </cell>";
        echo "<cell>" . $document->title ." </cell>";
        echo "<cell>" . $level . "</cell>";
        echo "<cell>" . $parent . "</cell>";
        echo "<cell>true</cell>";
        echo "<cell>false</cell>";
        echo "</row>";
    echo "</rows>";

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Thanks in advance for any help.