Windows Update Removes Commonwealth 2006 DST Changes

A new Windows Update applied this morning, which according to this knowledge base item, it "remove the Australian daylight saving time 2006 912475 update".

Daylight saving time changes to standard time on last Sunday of March, 2007. Therefore, computers that have the KB 912475 update installed will not show the correct 2007 daylight saving time transition date for the affected time zones in Australia. These computers will change from daylight saving time to standard time a week late, on April 1, 2007.

I have previously blogged about that KB 912475 change, which was caused by Commonwealth Game 2006 in Melbourne finished on the same day of DST change. Apparently Microsoft Windows is not capable of managing DST change exception just for one year. Therefore in order to display the correct time in 2007, Microsoft is pushing out another automated update to revert back to the old behaviour.

I think it must be very confusing to software packages that keeps internal data in GMT/UTC, and apply the local time when it needs to be displayed. For example a diary/event scheduler. An event created between 26 March and 2 April 2006 will have the correct local time offset with KB 912475 applied -- but after KB 913670 has been applied it will use the wrong offset.

I guess it is not uncommon for MS to break one patch with another patch.

At least Linux timezone file is unaffected as it takes care of the exception years.