Index: meta.php
===================================================================
--- meta.php	(revision 31261)
+++ meta.php	(working copy)
@@ -1351,8 +1351,12 @@
 		// We prefer to avoid joins if possible. Look for an existing join compatible with this clause.
 		$alias = $this->find_compatible_table_alias( $clause, $parent_query );
 		if ( false === $alias ) {
-			$i = count( $this->table_aliases );
-			$alias = $i ? 'mt' . $i : $this->meta_table;
+			if( empty( $parent_query['alias'] ) ){
+				$i = count( $this->table_aliases );
+				$alias = $i ? 'mt' . $i : $this->meta_table;
+			} else {
+				$alias = $parent_query['alias'];	
+			}
 
 			// JOIN clauses for NOT EXISTS have their own syntax.
 			if ( 'NOT EXISTS' === $meta_compare ) {