Just got the N7 for the wife to test out, she notices when the screen is off for a while in sleep mode, and she hits the power button to wake it up it does not wake up right away, she sometimes has to do it 2 or 3 times, or it won't wake at all and then she has to hold the power button down, then when it wakes up, she has to back out to get out of powering down. Is this normal.