To get best results of jQuery Mobile styles of contents inside page, dialog, panel or popup, always place them inside data-role="content"
.
<div data-role="popup" id="popupMenu" data-theme="d">
<div data-role="content">
<ul data-role="listview" data-inset="true" data-theme="d" data-filter="true">
<!-- list items -->
</ul>
</div>
</div>