Thank you all. I tried several lens/camera/exposure combinations this morning and found only my most expensive 24-105 Canon L lens produced this problem and only when I have (relatively) bright light in the subject. Most disappointed that the lens does not manage the internal reflections better. Though on balance I still like my new lens.
Test combinations included 40D, 6D - Canon 24-105L, Canon 75-300, Samyang 14.