This is not really a bug but a limitation of the dual time zone display when daylight time goes into effect, and to a lesser degree, when we revert to standard time. Apparently, it's not a very common problem since very few people complain about it, but it's interesting.
When you use dual time zones in Outlook and the default zone is west of the secondary zone, an extra hour is added to the time scale offset for the Sunday DST goes into effect. If you view multiple dates and begin with that Sunday, the (incorrect) offset is used on the time scale so it appears Outlook has the times wrong.
For example, if your default time zone is Pacific and Eastern is your secondary time, when Sunday rolls around, the time scale incorrectly displays a 4 hr time difference all day. If you use a multi-day view with Sunday as the first day, the Sunday time scale is used, so it appears there is a 4 hour time difference each day.
This view anomaly occurs because the default is a zone west of the secondary and Outlook takes into consideration that DST goes into effect in the earlier time zone and adjusts the times using the wrong offset. The entire 24 hour period uses the same offset and the first day in the view determines the offset. This issue also affects the view when the time 'falls back' to standard time, but only if the dual time zones are 3 or more hours apart.
Fortunately Outlook uses GMT and time zone offsets to calculate appointment times and reminders are based off the default time zone, not the secondary zone, so it's unlikely to cause missed appointments (if you use reminders). When you open the appointments they appear at the correct time.
"Time heals all wounds" and it will fix this display problem - until then, use the work week view if you use the dual time zone feature and the default zone is west of the secondary zone.
DST Starts or Ends on different dates
When the two time zones start and/or end Daylight Saving time on different dates, the time scale will vary during the delta period. For example, Helsinki starts DST at the end of March while the US makes the change 2 weeks earlier, so during this 2 week period, the usual difference will be off by an hour, depending on which zone is set as primary. In the fall, there is a 1 week lag where the times will be off by an hour.
Outlook 2010 Dual time Swap bug
When you use Outlook 2010’s dual time zone feature and one time zone uses DST and the other does not, when you swap zones the Use DST checkbox in Window’s Date and Time applet may be unchecked when the time zone that uses DST is active. Because Outlook 2010 doesn’t display the Use DST checkbox, you won’t know this unless you happen to notice the computer’s time is off an hour.
Solution: Install Outlook 2010 SP1.
If you are having other appointment problems relating to time zones, see //support.microsoft.com/kb/928388 for more information.