Git bisected the Emacs repo at Savannah to:

046fb9fbdc0ee0c26e0063ce5ee94bead46ee98d is the first bad commit
commit 046fb9fbdc0ee0c26e0063ce5ee94bead46ee98d
Author: Dmitry Antipov <dmantipov@yandex.ru>
Date:   Tue Dec 11 13:51:12 2012 +0400

    * buffer.c (Fset_buffer_multibyte): Do not force redisplay
    if changed buffer is not shown in a window.
    * insdel.c (prepare_to_modify_buffer): Likewise.
    * window.c (replace_buffer_in_windows_safely): Do nothing
    if buffer is not shown in a window.
    (Fforce_window_update): Likewise if string or buffer argument
    is passed.

:040000 040000 c3cd9f89a3926ca04ecfee03ae667056986ba352
385c925b8bcfcc59262a140e4ce8701b20eb7265 M      src