Struts2 JQuery Grid: Missing tooltips on header

Question

So I've taken over an old project with Struts2 (2.3.32) with struts2-jquery-grid-plugin-3.7.1. There is a grid that is working well. Only problem, is that the table header is missing the tooltips. They are important, since the columns are narrow and have abbreviated titles. I've never worked with jquery grid, so i've no clue where to start.

I've tried with the tooltip and label attributes (see the "test" string) and with javascript (the TODO came from the former dev, but doesn't work either). Interestingly it shows the tooltips for all the other cells on hover, displaying the value in the cell. I'd expect to at least do the same for the header, but it doesn't.

<sjg:grid
    id="gridedittable"
    loadonce="false"
    caption="Werbemittel Schnellerfassung" 
    dataType="json" 
    href="%{remoteurl}" 
    footerrow="true"
    pager="true" 
    navigator="true"
    navigatorSearchOptions="{sopt:['eq','ne','lt','gt']}"
    navigatorAddOptions="{height:280,reloadAfterSubmit:true}"
    navigatorEditOptions="{height:280,reloadAfterSubmit:false}"
    navigatorEdit="false"
    navigatorView="false"
    navigatorDelete="false"
    navigatorAdd="false"
    navigatorSearch="false"
    navigatorDeleteOptions="{height:280,reloadAfterSubmit:true}"
    gridModel="gridModel"
    rowList="20,30,50,100"
    rowNum="20"
    editurl="%{editurl}"
    editinline="true"
    onSelectRowTopics="rowselect"
    viewrecords="true"
    height="450">

...

    <s:iterator value="#ads.values()" var="ads" status="adStatus">
        <sjg:gridColumn name="advertisingMap.%{#ads.itemId}" index="%{shortName}" title="%{shortName}" width="50" editable="true" edittype="text" sortable="false" search="false" tooltip="test" label="test"/> <!-- TODO: Add tooltip onmouseover="javascript:tooltip.show('test');" onmouseout="javascript:tooltip.hide();" -->
    </s:iterator>
</sjg:grid>