Here's a fix for your problem..And loads of other problems including YouTube hanging and such,
I just fixed this on my GF's phone. It's probably been a problem since a recent OS update. Old stuff usually lingers. So here's the solution:
1 Turn off your phone
2 Hold down the power button, the Home button and the Volume Up byttons to enter recovery mode.
3 Using the volume up/down buttons, navigate to "wipe cache partition"(cant recall the name clearly but it should be something similar. Remember, you wanna wipe the cache not anything else.) and press the power button to execute.
4 Restart the phone from the same menu
She made me lasange for doing this, it's well worth the trouble