Perhaps this should be a bug report.
When you copy a one hour event to create a new one hour event, the calendar starts the event seven hours earlier than intended, ends the event when intended, making the event last for eight hours total. I reset the default event time to two hours, and still got an event lasting 8 hours. I reset the default to one hour, and continue to have eight hour events when copying.
Note that creating new events works as expected.