To solve this issue you have to specifically add background images for iOS 6, Follow following steps to add this using new xCode.
1) Add new image set from asset catalog and name it "Default" image set
2) Right click on that asset catalog image.
3) Choose iPhone, Retina 4 - inch from options like following
4) Add images in sequence with resolutions
320 * 480
640 * 960
640 * 1136
5) Clean your project
6) Run your project
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