diff --git a/system/database/DB_query_builder.php b/system/database/DB_query_builder.php
index a734603..0d04213 100644
--- a/system/database/DB_query_builder.php
+++ b/system/database/DB_query_builder.php
@@ -2557,18 +2557,22 @@
 			return;
 		}
 
-		foreach ($this->qb_cache_exists as $val)
+		$parts = array_unique($this->qb_cache_exists); // select, from, etc.
+
+		foreach ($parts as $val)
 		{
 			$qb_variable	= 'qb_'.$val;
 			$qb_cache_var	= 'qb_cache_'.$val;
 
-			if (count($this->$qb_cache_var) > 0)
+			$qb_new = $this->$qb_cache_var;
+
+			foreach ($this->$qb_variable as $qb_var)
 			{
-				foreach ($this->$qb_cache_var as &$cache_var)
-				{
-					in_array($cache_var, $this->$qb_variable, TRUE) OR $this->{$qb_variable}[] = $cache_var;
-				}
+			 	in_array($qb_var, $qb_new, TRUE) OR $qb_new[] = $qb_var;
 			}
+			
+			$this->$qb_variable = $qb_new;
+
 		}
 
 		// If we are "protecting identifiers" we need to examine the "from"