I think this is a type of out-of-focus blur, because the double edge on affected petals gets more prominent as it ismore distalfrom the focus area. This is much more obvious on full frame bodies because they provide more shallow DOF. I had a similar experience when I put a 100 2.8 macro on a 5D Mk2 for the first time, butnever thoughtmuch about it.


IS would haveblurred the whole thing. A UV filter would have caused flare more likely.


If you want to find out for yourself, try to reproduce the effect and then see if it goes away when you use smaler apertures.


Take care.