"Scanlines" in Bokeh?

[bbailey]

This may just be me obsessing, but I took some images yesterday with the 20D and 100-400 and I noticed something strange.

In two bird shots with water as the background, certain parts of the out of focus areas appear to have faint horizontal lines running across them. The smaller the image is viewed, the more apparent it seems. I don't know if it was just the pattern of the water creating weird highlights, or something weird with the equipment. This is the only time I've noticed this, and it only seems to be in a few shots from that day.

I figured I would ask here since someone probably knows if this was just the water wreaking havoc on the bokeh or not.

Below are two images with the effect I'm talking about most visible (but still faint) on the left side of the frame.

[dbphotos]

I don't see them on the first one but I definitely see them on the second image. I don't think it takes away from the image however. I will leave the technical answers to other Canon users, maybe they have experienced it. Does that lens have IS?

[bbailey]

Thanks.

Yes, the lens has IS, but it was only turned on for the second image.