prevent false freeing of vector

src/frontend/parse.c

@@ -471,7 +471,7 @@ void free_pnode_x(struct pnode *t)
         free_pnode(t->pn_right);
         free_pnode(t->pn_next);
         tfree(t->pn_name); /* va: it is a copy() of original string, can be free'd */
-        if (t->pn_value && !(t->pn_value->v_flags & VF_PERMANENT)) {
+        if (t->pn_use == 1 && t->pn_value && !(t->pn_value->v_flags & VF_PERMANENT)) {
             vec_free(t->pn_value); /* patch by Stefan Jones */
         }
         txfree(t);