I don't know if this is really a bug or a feature, but it seems that meeting attendees can change the time for a meeting in their local calendar. The person that invited to the meeting gets a notification of this change, but his meeting time remains the same.
If this is a feature to allow attendees to make a suggestion for alternative meeting times or let them chose to attend to only e.g. half of the meeting, the invitee should see such changes made by the invitee in his own interface.
I don't know if this behaviour is the way Exchange does it, but the Groupware solution we used to have (MeetingMaker) allowed no changes for the attendees.
A little feature request: The button "calendar" offered in meeting invitation emails shows the event in your calendar. This "virtual" event should be distinguishable from the other events, e.g. with a dotted frame.