> 2006-01-27 textmodes/flyspell.el
 >   (flyspell-incorrect, flyspell-duplicate): Doc fix.

Rather than reverting I'd propose to fix that as in the attached patch.
That patch also simplifies the corresponding code and fixes a bug you
should be able to reproduce as follows:

(1) Set `flyspell-duplicate-distance' to 12 and enable `flyspell-mode'.

(2) In an empty buffer insert the single line:

worryin and worryin

Both occurrences of "worryin" should get highlighted with
`flyspell-duplicate' face.

(3) Correct the second occurrence of "worryin" to "worrying".  Thus your
line should read as:

worryin and worrying

with the highlighting removed from the second occurrence.

(4) Moving the cursor to the first "worryin" should get you now

Error in post-command-hook: (error Invalid search bound (wrong side of point))

virtually disabling `flyspell-mode'.


The bug is caused within

(defun flyspell-word-search-forward (word bound)
   (save-excursion
     (let ((r '())
	  (inhibit-point-motion-hooks t)
	  p)
       (while (and (not r) (setq p (search-forward word bound t)))
	(let ((lw (flyspell-get-word '())))
	  (if (and (consp lw) (string-equal (car lw) word))
	      (setq r p)
	    (goto-char (1+ p)))))
       r)))

Note that the string " and worryin" contains exactly 12 characters.
`search-forward' stops after having found the second "worryin" but the
subsequent conditional fails since "worrying is correct".  `bound' still
refers to the position after "worryin" but `point' gets set to the
position after "worrying" raising the wrong side of point error.