=== modified file 'lisp/mouse.el'
--- lisp/mouse.el	2010-08-29 16:17:13 +0000
+++ lisp/mouse.el	2010-09-05 14:07:38 +0000
@@ -43,7 +43,10 @@
   :group 'mouse)
 
 (defcustom mouse-drag-copy-region nil
-  "If non-nil, mouse drag copies region to kill-ring."
+  "If non-nil, copy to kill-ring upon mouse adjustments of the region.
+
+This affects `mouse-save-then-kill' (\\[mouse-save-then-kill]) in
+addition to mouse drags."
   :type 'boolean
   :version "24.1"
   :group 'mouse)
@@ -1348,8 +1351,13 @@
 have selected whole words or lines, move point or mark to the
 word or line boundary closest to CLICK instead.
 
+If `mouse-drag-copy-region' is non-nil, this command also saves the
+new region to the kill ring (replacing the previous kill if the
+previous region was just saved to the kill ring).
+
 If this command is called a second consecutive time with the same
-CLICK position, kill the region."
+CLICK position, kill the region (or delete it
+if `mouse-drag-copy-region' is non-nil)"
   (interactive "e")
   (mouse-minibuffer-check click)
   (let* ((posn     (event-start click))
@@ -1371,7 +1379,11 @@
      ((and (eq last-command 'mouse-save-then-kill)
 	   (eq click-pt mouse-save-then-kill-posn)
 	   (eq window (selected-window)))
-      (kill-region (mark t) (point))
+      (if mouse-drag-copy-region
+          ;; region already saved the previous click,
+          ;; don't make a duplicate entry, just delete
+          (delete-region (mark t) (point))
+        (kill-region (mark t) (point)))
       (setq mouse-selection-click-count 0)
       (setq mouse-save-then-kill-posn nil))
 
@@ -1394,6 +1406,9 @@
 	  (goto-char (nth 1 range)))
 	(setq deactivate-mark nil)
 	(mouse-set-region-1)
+        (when mouse-drag-copy-region
+          ;; presumably region already copied to kill-ring once, so replace.
+          (kill-new (filter-buffer-substring (mark t) (point)) t))
 	;; Arrange for a repeated mouse-3 to kill the region.
 	(setq mouse-save-then-kill-posn click-pt)))
 
@@ -1405,6 +1420,8 @@
 	(if before-scroll (goto-char before-scroll)))
       (exchange-point-and-mark)
       (mouse-set-region-1)
+      (when mouse-drag-copy-region
+        (kill-new (filter-buffer-substring (mark t) (point))))
       (setq mouse-save-then-kill-posn click-pt)))))