No, what it should do is:
- when timer ends or stop button is pressed it should turn off microwaves but keep spinning until original position
- when door is opened just stop everything immediately
This way you can stop the plate manually at any position but when operating microwave in the usual way you get the benefit of the cup always pointing the right way.
Most microwaves I use (at home and work) have 30sec increment buttons so I always stick to 10 second increments and no, they don't end when they started.