Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 7616)
+++ wp-includes/widgets.php	(working copy)
@@ -614,6 +614,8 @@
 		}
 
 		foreach ( (array) $_POST['widget-text'] as $widget_number => $widget_text ) {
+			if ( !isset($widget_text['text']) && isset($options[$widget_number]) ) // user clicked cancel
+				continue;
 			$title = strip_tags(stripslashes($widget_text['title']));
 			if ( current_user_can('unfiltered_html') )
 				$text = stripslashes( $widget_text['text'] );
@@ -750,6 +752,8 @@
 		}
 
 		foreach ( (array) $_POST['widget-categories'] as $widget_number => $widget_cat ) {
+			if ( !isset($widget_cat['title']) && isset($options[$widget_number]) ) // user clicked cancel
+				continue;
 			$title = trim(strip_tags(stripslashes($widget_cat['title'])));
 			$count = isset($widget_cat['count']);
 			$hierarchical = isset($widget_cat['hierarchical']);
@@ -1170,6 +1174,8 @@
 		}
 
 		foreach( (array) $_POST['widget-rss'] as $widget_number => $widget_rss ) {
+			if ( !isset($widget_rss['url']) && isset($options[$widget_number]) ) // user clicked cancel
+				continue;
 			$widget_rss = stripslashes_deep( $widget_rss );
 			$url = sanitize_url(strip_tags($widget_rss['url']));
 			$options[$widget_number] = wp_widget_rss_process( $widget_rss, !isset($urls[$url]) );
@@ -1460,6 +1466,8 @@
 
 		foreach ( (array) $_POST['widget-many'] as $widget_number => $widget_many_instance ) {
 			// compile data from $widget_many_instance
+			if ( !isset($widget_many_instance['something']) && isset($options[$widget_number]) ) // user clicked cancel
+				continue;
 			$something = wp_specialchars( $widget_many_instance['something'] );
 			$options[$widget_number] = array( 'something' => $something );  // Even simple widgets should store stuff in array, rather than in scalar
 		}
Index: wp-includes/script-loader.php
===================================================================
--- wp-includes/script-loader.php	(revision 7616)
+++ wp-includes/script-loader.php	(working copy)
@@ -187,7 +187,7 @@
 				'saveText' => attribute_escape(__('Save »')),
 				'confirmText' => __("Are you sure you want to delete the file '%title%'?\nClick ok to delete or cancel to go back.")
 			) );
-			$this->add( 'admin-widgets', '/wp-admin/js/widgets.js', array( 'interface' ), '20080319' );
+			$this->add( 'admin-widgets', '/wp-admin/js/widgets.js', array( 'interface' ), '20080407c' );
 			$this->localize( 'admin-widgets', 'widgetsL10n', array(
 				'add' => __('Add'),
 				'edit' => __('Edit'),
Index: wp-admin/js/widgets.js
===================================================================
--- wp-admin/js/widgets.js	(revision 7616)
+++ wp-admin/js/widgets.js	(working copy)
@@ -11,7 +11,7 @@
 		var widgetAnim = $.browser.msie ? function() {
 			var t = $(this);
 			if ( t.is(':visible') ) {
-				if ( disableFields ) { t.find( ':enabled' ).not( '[name="widget-id[]"], [name*="[submit]"]' ).attr( 'disabled', 'disabled' ); }
+				if ( disableFields ) { t.find( ':input:enabled' ).not( '[name="widget-id[]"], [name*="[submit]"]' ).attr( 'disabled', 'disabled' ); }
 				li.css( 'marginLeft', 0 );
 				t.siblings('h4').children('a').text( widgetsL10n.edit );
 			} else {
@@ -25,7 +25,7 @@
 			var t = $(this);
 
 			if ( t.is(':visible') ) {
-				if ( disableFields ) { t.find( ':enabled' ).not( '[name="widget-id[]"], [name*="[submit]"]' ).attr( 'disabled', 'disabled' ); }
+				if ( disableFields ) { t.find( ':input:enabled' ).not( '[name="widget-id[]"], [name*="[submit]"]' ).attr( 'disabled', 'disabled' ); }
 				if ( width > 250 )
 					li.animate( { marginLeft: 0 } );
 				t.siblings('h4').children('a').text( widgetsL10n.edit );