"add media" media browser not encapsulated in overlay

After upgrading to 7.x-1.0-beta8 and Media 7.x-1.3, the media browser pop-up is no longer enclosed by the overlay divs. Directly under , we get:

<div class="ui-dialog ui-widget ui-widget-content ui-corner-all media-wrapper" style="display: block; z-index: 10002; outline: 0px none; height: auto; width: 800px; top: 315px; left: 141px;" tabindex="-1" role="dialog" aria-labelledby="ui-dialog-title-mediaBrowser">
<iframe id="mediaBrowser" class="media-modal-frame ui-dialog-content ui-widget-content" width="800px" scrolling="auto" src="/media/browser?render=media-popup&types%5Baudio%5D=audio&types%5Bimage%5D=image&types%5Bvideo%5D=video&activePlugins=&id=media_gallery&multiselect=true&plugins=undefined" style="width: 800px; min-height: 0px; height: 550px;">

There are no overlay divs or classes, such as appear in working overlays, e.g.

<div id="overlay-container">
<div class="overlay-modal-background"></div>
<iframe class="overlay-element" scrolling="auto" frameborder="0" allowtransparency="true" tabindex="-1">

This is not just a visual issue. The media browser is non-functional in this form. Media can be uploaded, but do not appear in the gallery. The library doesn't work at all.

Note that I have applied the patch in #1939186: Two media browsers, but this issue was occuring before that.