Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 57483)
+++ wp-includes/user.php	(working copy)
@@ -2371,7 +2371,18 @@
 		if ( $user_email !== $old_user_data->user_email || $user_pass !== $old_user_data->user_pass ) {
 			$data['user_activation_key'] = '';
 		}
-		$wpdb->update( $wpdb->users, $data, array( 'ID' => $user_id ) );
+
+		$data_changed = false;
+		foreach ( $data as $key => $value ) {
+			if ( isset( $old_user_data->{$key} ) && $old_user_data->{$key} !== $value ) {
+				$data_changed = true;
+				break;
+			}
+		}
+
+		if ( $data_changed ) {
+			$wpdb->update( $wpdb->users, $data, array( 'ID' => $user_id ) );
+		}
 	} else {
 		$wpdb->insert( $wpdb->users, $data );
 		$user_id = (int) $wpdb->insert_id;