After many hints and tries, someone actually found out the mistake in the photo. Apparently the photographer, who shot the picture, used some Photoshop software to touch up the photo and in the process did something very weird.
Image Source: www.scoopwhoop.com
If you haven’t still found the mistake, look at the leg of the model sitting on the right. See it!! She has two right feet. However, the singer herself tweeted a pic of herself showing her two normal feet. Here is that image.
Image Source: www.fbcdn.net