UI Distortions in iOS device running OS 4.2
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I am working on a iOS app where we need to provide support for device OS from 4.2. While I am doing testing, my app in old device (iPod or iPhone - non retina) having 4.3 OS, sometimes UI distortion occurs. I have some custom view animations in my app and they don't perform well in the old device. Some times I see buttons at wrong place when I make a navigation call in the app. Is this issue with old OS or issue with old hardware? I don't see these issues in new devices running iOS 5.0 and above. Please help me.

Thanks.