Index: src/wp-includes/option.php
===================================================================
--- src/wp-includes/option.php	(revision 26899)
+++ src/wp-includes/option.php	(working copy)
@@ -494,18 +494,19 @@
 	} else {
 		$transient_timeout = '_transient_timeout_' . $transient;
 		$transient = '_transient_' . $transient;
-		if ( false === get_option( $transient ) ) {
-			$autoload = 'yes';
-			if ( $expiration ) {
-				$autoload = 'no';
-				add_option( $transient_timeout, time() + $expiration, '', 'no' );
-			}
-			$result = add_option( $transient, $value, '', $autoload );
-		} else {
-			if ( $expiration )
-				update_option( $transient_timeout, time() + $expiration );
-			$result = update_option( $transient, $value );
-		}
+		$autoload = 'yes';
+		
+                if ( false != get_option( $transient ) ) {
+                        delete_option( $transient );
+                        delete_option( $transient_timeout );                    
+                }
+                
+                if ( $expiration ) {
+                        $autoload = 'no';
+                        add_option( $transient_timeout, time() + $expiration, '', 'no' );
+                }
+                
+                $result = add_option( $transient, $value, '', $autoload );
 	}
 	if ( $result ) {
 		do_action( 'set_transient_' . $transient, $value, $expiration );