Yes indeed it is a bug. We've patched it and updated the firmware. If you would update now, setting the power state should work. Thanks for reporting the bug.
FYI, when the controller is in "standby" mode, it just does not water. Other functions should work i.e. garage door. Or if you had set your winter season to 0%, it won't water. The power button should be seldom used, except for emergency turn off.