HDR feature on iPhone 4 Camera is not working as expected.

I have had my iPone for six months now. The camera has worked admirably. Recently,when using it in HDR mode, it has begun to generate two nearly identical images for every exposure, the tonal spread is different in each: the first is lightened, the second is darker. It seems they need to be combined for best results, but I don;t recall having this problem earlier. Anyone have this problem? Is there a solution or is something amiss with the iPhone?