bug#13982: 24.2; Bug in function format-time-string when used under Windows

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 19 Mar 2013 12:56:30 +0200
> From: Bostjan Vilfan <bjvilfan@gmail.com>
> Cc: 13982@debbugs.gnu.org
> 
> Hello, and thanks for your message. I did as per your instructions,
> and the value of
> 
>  (format-time-string "%H:%M %z %Z")
> 
> is "12:30 +0200 CDT" (actual local time was 11:30; so in other words
> emacs thinks local time is 1 hour ahead of actual local time)
>
> Your remark that all your Windows machines give the correct answer
> indicates that there must be some settings on my computer that is at
> fault; but I have no idea what that is.

I don't think there's a Windows time zone whose name is "CDT".  Can
you check if you happen to have a TZ variable in the environment, and
if so, what's its value?  Please look both in the Computer's
Properties and in the command shell from which you invoke "emacs -Q".

Also, I asked you to tell which time zone do you see in the Date/Time
dialog of your Windows system.  Right-click on the time display in the
right corner of your task bar, and select "Adjust date/time".  In the
dialog that pops, click "Change timezone", and tell the name of your
current Windows time zone that is shown in the middle of the dialog.

If the Windows time zone and the time zone given to Emacs are
different, you can have all kinds of "1 hour off" problems, especially
around daylight savings change date.

> I made one additional experiment: the version of emacs I was using was
> a modification by Vincent Goulet
> (http://vgoulet.act.ulaval.ca/en/emacs/). I thought that in some way
> that version made some hidden changes, so I completely uninstalled it,
> and installed the version obtainable from the GNU site. The result of
> evaluating the above form was the same.

Which leaves your system as the prime suspect.