Sigma 35mm on Canon5D2. I've noticed this effect a few times with this lens. With the Canon 35mmL never saw it. I have used the Sigma 30 1.4, sigma 10-20 4.5-5.6, and the 150 macro as well and all seemed to have disturbing flare. the 10-20 being the worst the 150 being the best. No filter, with hood camera turned top left.
Wow, thanks for posting! There you go, there must be a real technical reason behind this flare, and it's related to the 5D MkII and a few Sigma lenses as we know so far. Holding the camera by the grip (with the top of the camera facing left) can produce the flare with light sources just outside the right hand side of the frame.
I'm pretty sure there is an internal reflection occurring in the camera body. Not sure what causes it though (underside of the mirror assembly??), and whether the same can occur with Canon lenses (perhaps the Sigma's rear lens elements protrude further and scatter more light in the body)?