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Update 2998527 causes incorrect code lookups on past dates

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This article explains the problem where KB 2998527 causes incorrect code lookups on past dates when you use the TimeZoneInfo class in an application.

Original product version:   .NET Framework 4.6, 4.5
Original KB number:   3012229

Symptoms

After October 26, 2014, applications that are hosted on systems that have the September 2014 Russian time zone update (KB 2998527) installed and that use the Microsoft .NET Framework might calculate time incorrectly when they use the TimeZoneInfo class.

This problem occurs in the following time zones:

  • (UTC-04:30) Caracas
  • (UTC+01:00) Windhoek
  • (UTC+02:00) Kaliningrad (RTZ 1)
  • (UTC+02:00) Tripoli
  • (UTC+03:00) Minsk
  • (UTC+03:00) Moscow, St. Petersburg, Volgograd (RTZ 2)
  • (UTC+05:00) Ekaterinburg (RTZ 4)
  • (UTC+06:00) Novosibirsk (RTZ 5)
  • (UTC+07:00) Krasnoyarsk (RTZ 6)
  • (UTC+08:00) Irkutsk (RTZ 7)
  • (UTC+09:00) Yakutsk (RTZ 8)
  • (UTC+10:00) Magadan
  • (UTC+10:00) Vladivostok, Magadan (RTZ 9)
  • (UTC+13:00) Samoa

Cause

This problem occurs because a change in the base offset of a time zone breaks any code in the affected time zones if that code looks up past dates by using TimeZoneInfo in the .NET Framework. This is because the .NET Framework can't track year-to-year changes in the base offset.

This problem was exposed by the recent changes to Russian time zones that are described in Microsoft Knowledge Base article 2998527.

The .NET Framework previously ignored the UTC offset that is set in an internal adjustment rule. Instead, it used the base UTC offset in certain calculations. The .NET Framework also ignored adjustment rules that don't have daylight transitions.

Status

Microsoft is researching this problem and will post more information in this article when the information becomes available. A new update is planned that will update the .NET Framework to correctly use UTC offsets and adjustment rules for all-time zones.

We recommend that you install both update 2998527 and the new update when it's available. This will make sure that UTC offset rules are used correctly for all past years and all years going forward.

More information

Consider the following C# example code:

TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("Russian Standard Time");
DateTime dt = TimeZoneInfo.ConvertTimeFromUtc(new DateTime(2013, 6, 1), tz);
Console.WriteLine(dt);

For example, before you apply KB 2998527, this code correctly returns the date and time as June 1, 2013 at 04:00. After you apply the update, the code incorrectly returns the date and time as June 1, 2013 at 03:00.