media plugin 0.60 beta でバグに遭遇。
github のソースを真似て次の用に直した。

--- davidpersson-media-cdeaec0/views/helpers/medium.php	Sun Jul 05 05:09:38 2009
+++ media/views/helpers/medium.php	Fri Dec 18 11:21:34 2009
@@ -108,4 +108,5 @@
 		foreach (Configure::read('Media.filter') as $type) {
-			$this->_versions += array_keys($type);
+			$this->_versions += $type;
 		}
+		$this->_versions = array_keys($this->_versions);