Index: src/wp-includes/js/mce-view.js
===================================================================
--- src/wp-includes/js/mce-view.js	(revision 31559)
+++ src/wp-includes/js/mce-view.js	(working copy)
@@ -434,7 +434,7 @@
 			if ( _.isObject( content ) && content.body.indexOf( '<script' ) !== -1 ) {
 				this.setIframes( content.head, content.body, callback, rendered );
 			} else if ( _.isString( content ) && content.indexOf( '<script' ) !== -1 ) {
-				this.setIframes( null, content, callback, rendered );
+				this.setIframes( '', content, callback, rendered );
 			} else {
 				this.getNodes( function( editor, node, contentNode ) {
 					content = content.body || content;
@@ -460,33 +460,27 @@
 		 * @param {Boolean}  rendered Only set for (un)rendered nodes. Optional.
 		 */
 		setIframes: function( head, body, callback, rendered ) {
-			var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver,
-				importStyles = this.type === 'video' || this.type === 'audio' || this.type === 'playlist';
+			var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver;
 
 			this.getNodes( function( editor, node, content ) {
 				var dom = editor.dom,
-					styles = '',
 					bodyClasses = editor.getBody().className || '',
 					iframe, iframeDoc, observer, i, resize;
 
 				content.innerHTML = '';
-				head = head || '';
 
-				if ( importStyles ) {
-					if ( ! wp.mce.views.sandboxStyles ) {
-						tinymce.each( dom.$( 'link[rel="stylesheet"]', editor.getDoc().head ), function( link ) {
-							if ( link.href && link.href.indexOf( 'skins/lightgray/content.min.css' ) === -1 &&
-								link.href.indexOf( 'skins/wordpress/wp-content.css' ) === -1 ) {
-
-								styles += dom.getOuterHTML( link ) + '\n';
-							}
-						});
-
-						wp.mce.views.sandboxStyles = styles;
-					} else {
-						styles = wp.mce.views.sandboxStyles;
+				tinymce.each( dom.$(
+					'link[rel="stylesheet"]',
+					editor.getDoc().getElementsByTagName( 'head' )[0]
+				), function( link ) {
+					if (
+						link.href &&
+						link.href.indexOf( 'skins/lightgray/content.min.css' ) === -1 &&
+						link.href.indexOf( 'skins/wordpress/wp-content.css' ) === -1
+					) {
+						head += dom.getOuterHTML( link ) + '\n';
 					}
-				}
+				} );
 
 				// Seems Firefox needs a bit of time to insert/set the view nodes,
 				// or the iframe will fail especially when switching Text => Visual.
@@ -516,7 +510,6 @@
 							'<head>' +
 								'<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />' +
 								head +
-								styles +
 								'<style>' +
 									'html {' +
 										'background: transparent;' +
@@ -578,9 +571,7 @@
 						iframeDoc.body.className = editor.getBody().className;
 					}
 
-					if ( importStyles ) {
-						editor.on( 'wp-body-class-change', classChange );
-					}
+					editor.on( 'wp-body-class-change', classChange );
 
 					$( node ).one( 'wp-mce-view-unbind', function() {
 						observer.disconnect();
