Index: src/wp-admin/js/theme.js
===================================================================
--- src/wp-admin/js/theme.js	(revision 26628)
+++ src/wp-admin/js/theme.js	(working copy)
@@ -370,6 +370,7 @@
 themes.view.Themes = wp.Backbone.View.extend({
 
 	className: 'themes',
+	$overlay: $( 'div.theme-overlay' ),
 
 	// Number to keep track of scroll position
 	// while in theme-overlay mode
@@ -497,7 +498,7 @@
 		});
 
 		this.overlay.render();
-		this.$el.append( this.overlay.el );
+		this.$overlay.html( this.overlay.el );
 
 		this.overlay.screenshotGallery();
 
Index: src/wp-admin/themes.php
===================================================================
--- src/wp-admin/themes.php	(revision 26628)
+++ src/wp-admin/themes.php	(working copy)
@@ -180,6 +180,7 @@
 ?>
 
 <div class="theme-browser"></div>
+<div class="theme-overlay"></div>
 
 <?php
 // List broken themes, if any.