Index: src/wp-admin/js/editor.js
===================================================================
--- src/wp-admin/js/editor.js	(revision 29796)
+++ src/wp-admin/js/editor.js	(working copy)
@@ -76,6 +76,7 @@
 
 			DOM.removeClass( wrap_id, 'html-active' );
 			DOM.addClass( wrap_id, 'tmce-active' );
+			DOM.setAttrib( txtarea_el, 'aria-hidden', true );
 			setUserSetting( 'editor', 'tinymce' );
 
 		} else if ( 'html' === mode ) {
@@ -112,6 +113,7 @@
 
 			DOM.removeClass( wrap_id, 'tmce-active' );
 			DOM.addClass( wrap_id, 'html-active' );
+			DOM.setAttrib( txtarea_el, 'aria-hidden', false );
 			setUserSetting( 'editor', 'html' );
 		}
 		return false;