Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 4734)
+++ /CKEditor/trunk/CHANGES.html	(revision 4735)
@@ -101,4 +101,5 @@
 		<li><a href="http://dev.fckeditor.net/ticket/4709">#4709</a> : Fixed inconsistent scroll-bar behavior on IE.</li>
 		<li><a href="http://dev.fckeditor.net/ticket/4776">#4776</a> : Fixed preview page failed to open when relative URl contains in document.</li>
+		<li><a href="http://dev.fckeditor.net/ticket/4812">#4812</a> : Fixed 'Esc' key not working on dialogs in Opera.</li>
 		<li>Updated the following language files:<ul>
 			<li><a href="http://dev.fckeditor.net/ticket/4346">#4346</a> : Dutch;</li>
Index: /CKEditor/trunk/_source/plugins/dialog/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/dialog/plugin.js	(revision 4734)
+++ /CKEditor/trunk/_source/plugins/dialog/plugin.js	(revision 4735)
@@ -642,5 +642,5 @@
 
 				element.on( 'keydown', accessKeyDownHandler );
-				element.on( 'keyup', accessKeyUpHandler );
+				element.on( CKEDITOR.env.opera ? 'keypress' : 'keyup', accessKeyUpHandler );
 
 				// Prevent some keys from bubbling up. (#4269)
@@ -772,6 +772,5 @@
 				// Remove access key handlers.
 				element.removeListener( 'keydown', accessKeyDownHandler );
-				element.removeListener( 'keyup', accessKeyUpHandler );
-				element.removeListener( 'keypress', accessKeyUpHandler );
+				element.removeListener( CKEDITOR.env.opera ? 'keypress' : 'keyup', accessKeyUpHandler );
 
 				// Remove bubbling-prevention handler. (#4269)
@@ -1833,6 +1832,9 @@
 
 		keyProcessor = keyProcessor[keyProcessor.length - 1];
-		keyProcessor.keyup && keyProcessor.keyup.call( keyProcessor.uiElement, keyProcessor.dialog, keyProcessor.key );
-		evt.data.preventDefault();
+		if ( keyProcessor.keyup )
+		{
+			keyProcessor.keyup.call( keyProcessor.uiElement, keyProcessor.dialog, keyProcessor.key );
+			evt.data.preventDefault();
+		}
 	};