Screen Rotation new i Phone 6S Plus

Having recently purchased a new i Phone 6s plus for my wife l find there is a problem with it. If you go to messages and select a new message the screen will not rotate, but if you select a previous message and then select a new message it will. We went to our local Apple store yesterday and even they could not solve the problem. They think it is something to do with the latest OSI upgrade. My i Phone 6 will rotate when you select a new message. Its great when you spend £699 for a new phone and it has faults. It seems that Apple is following Microsoft in not checking upgrades for bugs before releasing it. The only advice that the Apple store could suggest is to wait for the next upgrade and hope that fixes the fault. Not really happy with that but what else can l do.

Graham J