Index: uc_restrict_qty.module
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/uc_restrict_qty/uc_restrict_qty.module,v
retrieving revision 1.1.4.5
diff -u -p -r1.1.4.5 uc_restrict_qty.module
--- uc_restrict_qty.module	20 Jan 2009 16:23:15 -0000	1.1.4.5
+++ uc_restrict_qty.module	26 Jan 2011 17:28:56 -0000
@@ -96,6 +96,16 @@ function uc_restrict_qty_add_to_cart($ni
       );
     }
   }
+  // If item is being restricted, remove any existing items of this product from
+  // the cart, so that if the item has attributes only the most recently added
+  // version of the product remains.
+  elseif ($data['restrict_qty']) {
+    foreach (uc_cart_get_contents() as $item) {
+      if ($item->nid == $nid) {
+        uc_cart_remove_item($nid, $item->cart_id, $item->data);
+      }
+    }
+  }
   return $result;
 }