--- content_taxonomy.module
+++ (clipboard)
@@ -141,7 +141,12 @@
               $node->taxonomy[$field['vid']][$tid] = $tid;
             }
           }
-        }        
+        } 
+				// perform test to see if taxonomy for this vid is empty
+				// if so set it to be explicitly empty
+				if (empty( $node->taxonomy[$field['vid']] )){
+					$node->taxonomy[$field['vid']][] = NULL;
+				}   
       }
       break;