behaviour of spin controls - reset to prev value when press back button ?

I thought I noticed something odd when trying tu use the Alarm app.

When you create a new timer and click on the minutes field you get the spin control (arrow at bottom and top of a number). I have been setting a value and then touching the back button expecting the value to change. But this is not the case. Back and BTN seem to be acting like a cancel. To take the new value you have to tap the centre of the screen to accept the new value.

Not noticed this before.