This bug concerns the X11 style drag copy (and middle mouse button paste) on
GNU emacs 23.  I noticed this problem on systems employing GTK, and haven't
had the opportunity to try other systems.

I have attached a ogv formatted video showing the problem.

Since I didn't have a working mic, here is a narration.

I open emacs using -q.  You can see the message:
This is GNU Emacs 23.3.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.1).
The system is Ubuntu 10.04.

I then proceed to drag over some text in the buffer.

I then left click a character moving the mouse _slightly_ downward.  The
message "Mark set" appears at the bottom of the buffer.

The last action is to move the mouse pointer elsewhere in the buffer and
middle click.  To my surprise the text is no-longer available.

Discussion:  some sequence of calls either leading to or because of the
mark-setting is blowing away the drag copy buffer.  The "mark set" message
does not seem like adequate warning or explanation for this.  Note that the
mouse movement was not sufficient to replace the drag-copy buffer with any
new text. Instead what was there is forgotten.  When I try to reproduce
emacs-like sensitivity in firefox (used as a gmail client) the text only
seems to be blown away when I moved the mouse enough to place some new text
there.  Furthermore, in firefox, if I accidently slip and move the mouse
while clicking the left button my drag copy buffer is not blown away as long
as I move the pointer back to its original position before releasing.

Cheers,

Andy

-- 
Andrew I. Schein
www.andrewschein.com