[tz] Possible bug in the tz database

[random832 at fastmail.us]

On Sat, Jun 6, 2015, at 21:36, Howard Hinnant wrote:
> But this data indicates that local time behaves as follows that morning:
> 
>     2010-11-07 01:59:59 MDT = 2010-11-07 07:59:59 UTC
>     2010-11-07 01:00:00 MST = 2010-11-07 08:00:00 UTC
>     2010-11-07 01:00:01 MST = 2010-11-07 08:00:01 UTC
>     …
>     2010-11-07 01:59:59 MST = 2010-11-07 08:59:59 UTC
>     2010-11-07 03:00:00 CST = 2010-11-07 09:00:00 UTC
>     2010-11-07 03:00:01 CST = 2010-11-07 09:00:01 UTC
> 
> However I believe the intended behavior is:
> 
>     2010-11-07 01:59:59 MDT = 2010-11-07 07:59:59 UTC
>     2010-11-07 02:00:00 CST = 2010-11-07 08:00:00 UTC
>     2010-11-07 02:00:01 CST = 2010-11-07 08:00:01 UTC

My system's zdump output:
America/North_Dakota/Beulah  Sun Mar 14 08:59:59 2010 UTC = Sun Mar 14
01:59:59 2010 MST isdst=0
America/North_Dakota/Beulah  Sun Mar 14 09:00:00 2010 UTC = Sun Mar 14
03:00:00 2010 MDT isdst=1
America/North_Dakota/Beulah  Sun Nov  7 07:59:59 2010 UTC = Sun Nov  7
01:59:59 2010 MDT isdst=1
America/North_Dakota/Beulah  Sun Nov  7 08:00:00 2010 UTC = Sun Nov  7
02:00:00 2010 CST isdst=0
America/North_Dakota/Beulah  Sun Mar 13 07:59:59 2011 UTC = Sun Mar 13
01:59:59 2011 CST isdst=0
America/North_Dakota/Beulah  Sun Mar 13 08:00:00 2011 UTC = Sun Mar 13
03:00:00 2011 CDT isdst=1

In general, it's probably more useful to rely on zdump output, rather
than working through interpreting the data by hand, for reasoning about
what behavior a given piece of timezone data actually produces.