This has happened to me more than once and somehow I think I'm not the only one. When Microsoft Exchange sends out calendar related email, it includes time-zone information in the text of the message. Good idea, right? Well, the implementation leaves something to be desired. For example, if the message contains the line:
When: Wednesday, March 28, 2012 3:00 PM-4:00 PM (GMT-06:00) Central Time (US & Canada).
what time would you guess the event occurs at? If you guessed 21:00 UTC (12+3+6) then you lose. The time zone offset is actually GMT-5 as the "text/calendar" attachment (not so) plainly shows. The problem is that the local time-zone of the sender was Central Daylight Time.