bug#2996: 23.0.92; Scrolling narrows region

[Sebastian Rose <sebastian_rose@gmx.de>]

Chong Yidong <cyd@stupidchicken.com> writes:
> I can't reproduce this.  Did you scroll using the mouse-wheel, the
> scroll-bar, or some other method?  Please provide a *precise* set of
> instructions for reproducing this bug, starting from emacs -Q.



Yes, sorry for being unclear. I indeed found, that this only happens
when I use the mousewheel (which I always do: scroll-bar-mode nil).


Here's the recipe:

1. emacs -Q

2. C-x C-f file 
   file should contain more than a screenfull of text.

3. Right-click somewhere in the window to produce an active region. If
   you didn't move point before this, the region starts at the very top
   of the buffer.

4. Right-click somewhere further down to see, that the region is
   resized. 

5. Scroll down using the mousewheel, until the point moves. This
   happens, when point touches the upper window border.

   The mark is now moved from the very top of the buffer, to the first
   visible line.


Starting from 2. somewhere towards the end of the buffer and scrolling
up (in step 4.) has the same effect.



Note, that this does _NOT_ happen, when using the scrollbars or C-v.

It _DOES_ happen, when using M-v

This does _NOT_ happen, when I set the mark (C-SPACE).


   | Way to scroll | direction | region is growing |
   |---------------+-----------+-------------------|
   | scrollbar     | down      | t                 |
   | mousewheel    | down      | nil               |
   | C-v           | down      | nil               |
   | scrollbar     | up        | t                 |
   | mousewheel    | up        | nil               |
   | M-v           | up        | nil               |



When the mark is set through C-SPACE:

   | Way to scroll | direction | region is growing |
   |---------------+-----------+-------------------|
   | scrollbar     | down      | t                 |
   | mousewheel    | down      | t                 |
   | C-v           | down      | t                 |
   | scrollbar     | up        | t                 |
   | mousewheel    | up        | t                 |
   | M-v           | up        | t                 |



What I expected to happen:

I simply expected the region to grow in either case (scrollbar, wheel,
C/M-v).

At least, I expected scrollbars and mousewheel to behave the same way.


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