End time automatically changes when you change the start time

When I want to reschedule the start time of an existing meeting notice the end time will be adjusted automatically.
For example:If the current start time for the meeting is 2pm and the end time is 3pm. Let's say that you want to now change the start time to 1pm.  When you do this, the end time will automatically adjust to 2pm (keeping the meeting 1 hr in duration).
This is not how I would expect this to work. When I originally made this change, I am assuming that the end time will stay at 3pm. Thus when I close the dialog box, I am not looking at the end time box, since I made my edit to the start time. It is not until I back in the calendar view (after I already sent out 1 reschedule notice) that I notice that the end time is incorrect.To correct this, I have to make another change to the end time, which will require sending out a second reschedule notice.
So I want to add a setting function that the end time will not be automatically modified  when the start time is reset.