Why do Calendar events end up in the wrong time zone?

I often am invited to calendar events from others in different time zones. When I add them to my calendar they end up showing at the time in the sender's time zone, not my time zone. For example an event ao 10:00 Pacific time shows up on my calendar at 10:00 Eastern time instead of 13:00 Eastern time. I have time zone support turned on on my Mac.