Mark the current node as the last-saved if buffer unmodified

vundo.el

@@ -771,15 +771,23 @@ This function modifies `vundo--prev-mod-list',
       (unless (eq (vundo--latest-buffer-state mod-list)
                   latest-state)
         (vundo--draw-tree mod-list))
-      ;; Highlight current node.
-      (vundo--highlight-node (vundo--current-node mod-list))
-      (goto-char (vundo-m-point (vundo--current-node mod-list)))
-      ;; Update the face of the last saved node.
-      (when-let (((and vundo-highlight-saved-nodes vundo--last-saved-idx))
-                 ((>= vundo--last-saved-idx 0))
-                 (last-saved-node (aref mod-list vundo--last-saved-idx))
-                 (pt (vundo-m-point last-saved-node)))
-        (put-text-property (1- pt) pt 'face 'vundo-last-saved))
+
+      (let ((current-node (vundo--current-node mod-list)))
+	;; Highlight current node.
+	(vundo--highlight-node current-node)
+	(goto-char (vundo-m-point current-node))
+	;; Update the face of the last saved node.
+	(when vundo-highlight-saved-nodes
+	  ;; if the associated buffer is unmodified, it is the latest
+	  ;; saved (although it will have no prev-saved-ts).
+	  (if (with-current-buffer orig-buffer (not (buffer-modified-p)))
+	      (setq vundo--last-saved-idx (vundo-m-idx current-node)))
+	  (when-let ((vundo--last-saved-idx)
+		     ((>= vundo--last-saved-idx 0))
+		     (last-saved-node (aref mod-list vundo--last-saved-idx))
+		     (pt (vundo-m-point last-saved-node)))
+	    (put-text-property (1- pt) pt 'face 'vundo-last-saved))))
+
       ;; Update cache.
       (setq vundo--prev-mod-list mod-list
             vundo--prev-mod-hash mod-hash