I don't know where do you live, but it's pretty common in the colder climate: it's the heat generated by your hands that is amplified by the flash of your camera.

I do a lot of photography and it's not the first time I see this and it's a bit frustrating because it makes the image ugly <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Here an example: