iPhone 4S, foggy, hazy photos in dark with flash

Hey everybody,

I try to take some photos in my pitch dark room in the evening and I noticed a strange thing. Sometimes the photos are clear and sometimes they are hazy, foggy. I don't know why, does anybody have any idea? I don't have case on my iphone, so it is full naked, and I think it isn't out of focus, because i focused the object where I thought it was. And I didn't move the phone when I took the photo. So the problem is: sometimes the photos are clear and sometimes are foggy in dark, night. Is my phone faulty?

I enclosed 2 samples photos, check them out. Thanks for your help!

First is clear:

http://imageshack.us/photo/my-images/214/fot26d.jpg/

Second is foggy:

http://imageshack.us/photo/my-images/189/fot27.jpg/