nested collapsible causes parent collapsible-set to close

Found in A4.
Only happening with collapsible SETS not collapsibles

Ex.

<div id="set" data-role="collapsible-set">
    <div id="colapse" data-role="collapsible">
        <h3>title</h3>
        <div>content</div>
        <div id="sub" data-role="collapsible">
            <h3>subtitle</h3>
            <div>bacon</div>
        </div>
    </div>
</div>
                
