Today, I noticed that when I receive a text while my iPhone is on sleep, the phone does not vibrate. I have my phone set on silent and vibrate is on. However, when I receive a text when my iPhone isn't asleep, the phone vibrates. Is the no vibration when asleep a bug? Or is something in my settings not correct? I really need it to vibrate when asleep because I am a frequent texter and I simply cannot drain the battery life by not closing it when I'm not using it. Thanks.