Index: wp-includes/meta.php
===================================================================
--- wp-includes/meta.php	(revision 18407)
+++ wp-includes/meta.php	(working copy)
@@ -422,6 +422,10 @@
 
 		$this->queries = array();
 
+		// Single meta queries shouldn't need to pass an array of arrays
+		if( isset( $meta_query['key'] ) || isset( $meta_query['value'] ) )
+			$meta_query = array( $meta_query );
+		
 		foreach ( $meta_query as $key => $query ) {
 			if ( ! is_array( $query ) )
 				continue;