Thanks for adding the shooting conditions.


This shot looks like a deliberate attempt to create flare. I don't think it's a fair test of how well the lens will control flare in normal situations. In general, you should avoid shooting into a bright light source like this. If you must include the sun, try to put it closer to the corner of the image. Try it without the filter attached.I think that the light is reflecting off the front element of the lens and bouncing back off the filter to create the flare pattern.


The 24-105L lens does show some flare at wide angles, according to Bryan's review: http://www.the-digital-picture.com/Reviews/Canon-EF-24-105mm-f-4-L-IS-USM-Lens-Review.aspx. You should be able to avoid this by recomposing the shot and using a slightly longer focal length.