Index: /CKEditor/trunk/_source/plugins/dialogui/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/dialogui/plugin.js	(revision 3105)
+++ /CKEditor/trunk/_source/plugins/dialogui/plugin.js	(revision 3106)
@@ -320,5 +320,5 @@
 						attributes = { 'class' : 'cke_dialog_ui_checkbox_input', type : 'checkbox' };
 					cleanInnerDefinition( myDefinition );
-					if ( elementDefinition.checked )
+					if ( elementDefinition[ 'default' ] )
 						attributes.checked = 'checked';
 					_.checkbox = new CKEDITOR.ui.dialog.uiElement( dialog, myDefinition, html, 'input', null, attributes );