bug#8400: 24.0.50; Strange selection behavior in Gnus Article buffer

[Stephen Berman <stephen.berman@gmx.net>]

1. emacs -Q
2. Carry out the steps in NEWS to return to the pre-24 selection behavior:
   Change `mouse-drag-copy-region' to t.
   Change `x-select-enable-primary' to t.
   Change `x-select-enable-clipboard' to nil.
3. M-x gnus, answer y to continue to the Group buffer despite no server
   being found, then type `B f' to browse a foreign server,
   e.g. news.gmane.org, select a group and open an article.
4. In the Article buffer select some text (it doesn't matter whether by
   double clicking with mouse-1 or by the keyboard, though if the latter
   then after selecting point should at the end of the selection to have
   the same situation as when selecting by the mouse).
5. Type `M-w'.
6. Switch to a writable buffer, and type `C-y'.

=> The yanked text is not the selection from step 4, but -- if the
selection was made from text following the article headers -- a region
of the Article buffer ending at the start of the selection and beginning
either just below the last header line, or possibly including one or
more header lines; if the selection is within the headers, the yanked
text is the region beginning at the start of the selection and ending
just below the headers.

If you type `M-y' after step 6, then the yanked text is replaced by the
text selected in step 4.  If step 5 is omitted, C-y in step 6 yanks the
selected text as usual.

I have only observed this selection behavior in Gnus Article buffers,
and there it is reliably reproducible.  (I have observed it for some
time, probably since the new selection changes were introduced, but
didn't try to find a reproducible recipe till now.)

In GNU Emacs 24.0.50.1 (i686-suse-linux-gnu, GTK+ Version 2.20.1)
 of 2011-03-30 on escher
Windowing system distributor `The X.Org Foundation', version 11.0.10800000
configured using `configure  '--without-toolkit-scroll-bars' 'CFLAGS=-g -O2 -fno-optimize-sibling-calls''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=local
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t