iPhone 5 garageband

I have an iphone 5 running the latest version of both ios and garageband and I'm noticing that the velocity key feature of garageband isn't working properly. For example when I have my phone resting on my bed it won't register the harder taps and thus make a louder sound. The only time it will do this is if I hold the phone in the air and accelerate it while pushing a key at the same time. I know the accelerometer works in my device so I'm wondering of this is a garageband/ios 6 problem or what it could be.

Cheers