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. 

Until Microsoft fixes this, you’ll need to open the Date and Time applet in Control Panel and enable Use DST  after swapping time zones.