I would like to report the following bug.
Open the attached file in Emacs, and move point to the first position.
Define a keyboard macro: (I want to put each line inside double-quotes)
"			;; self-insert-command
C-e			;; move-end-of-line
"			;; self-insert-command
C-a			;; message-beginning-of-line
<down>			;; next-line

Now ask Emacs to repeat this macro 49 times.
The result is wrong: at around line 35, the first double-quote
is no longer at the start of the line; then on successive lines
the position of the first inserted double-quote walks to the right.

-----------------------------------------------------------------
In GNU Emacs 24.5.1 (i686-apple-darwin, NS apple-appkit-1038.36)
  of 2015-04-10 on builder10-6.porkrind.org
Windowing system distributor `Apple', version 10.3.1038
Configured using:
  `configure --with-ns '--enable-locallisppath=/Library/Application
  Support/Emacs/${version}/site-lisp:/Library/Application
  Support/Emacs/site-lisp' --host=i686-apple-darwin
  --build=i686-apple-darwin --with-jpeg=no --with-png=no --with-gif=no
  --with-tiff=no'

Important settings:
   locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
   recentf-mode: t
   show-paren-mode: t
   tooltip-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Recent messages:
Cleaning up the recentf list...
File /Users/abbott/ShortTerm/EMACS-BUG-orig removed from the recentf list
Cleaning up the recentf list...done (1 removed)
Loading /Users/abbott/Work/CoCoA/CoCoA4/4.7/UI/emacs/cocoa.emacs...done
Loading  
/Users/abbott/Work/CoCoA/CoCoA5/CoCoALib-0.99/src/CoCoA-5/emacs/cocoa5.emacs...done
Loading rmail-spam-filter.elc...done
For information about GNU Emacs and the GNU system, type C-h C-a.
Defining kbd macro...
Keyboard macro defined
(Type e to repeat macro)

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr warnings emacsbug sendmail cl-extra
info magit-autoloads git-rebase-mode-autoloads git-commit-mode-autoloads
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mail-prsvr mailabbrev mail-utils gmm-utils mailheader ring pcvs-util
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multi-tty emacs)

Memory information:
((conses 8 143707 11759)
  (symbols 24 23822 0)
  (miscs 20 100 224)
  (strings 16 30397 6332)
  (string-bytes 1 745514)
  (vectors 8 14455)
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