Strange problem with emacs-lisp/copyright.el

[Lele Gaifax <lele@metapensiero.it>]

Hi all,

since a couple of week I switched my main development environment to Emacs
master, and I'm quite happy.

The only problem I had is one strange defect I'm hitting that, despite all my
efforts to reproduce it, I'm still unable to understand the nature. It seems
very similar to bug#2209, now archived.

In my setup I've configured

  (add-hook 'before-save-hook #'copyright-update)

to automatically update the copyright years range in files header. Accordingly
to the VC tool, I installed that setup more than one year ago and never
noticed any problem, with Emacs 25.

With the new Emacs, when I save multiple files that wasn't yet touched in the
current year, *sometime* and *some files* the new year is added in the wrong
location, that is the new year (that is, the string ", 2017") gets added
somewhere in the file, not where it should go: most of the times at the
beginning of a line, sometime in the middle, in any case apparently at the
`point' location, where the cursor was at save time.

As said, I've tried several times to understand what's going on, either with
edebug-ing the `copyright-update-year' function or decorating it with a few
`message' calls to emit the updated location and such, but it seems some sort
of eisenbug... I even reverted my source tree to the exact state before this
happened, and applied the very same set of mechanical replacements (I was
fixing a single typo and I used wgrep to spot and correct all instances), with
no luck.

Do this ring any bell, or can some one hints me on a better/more effective way
to investigate the issue, before opening a new bug report?

Thanks in advance,
ciao, lele.
-- 
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
lele@metapensiero.it  |                 -- Fortunato Depero, 1929.