Odd Appearance of Long Exposure in Water

Hi all,

I have a bunch of photos from a recent shoot at a local waterfall, and the bubbles in the water have an odd appearance in many (but seemingly not all) of the photos. It appears as if an individual bubble appears multiple times along a certain path rather than just a blurred streak. See the uploaded 100% crop. I'll also post the whole image for reference. Has anyone explain what causes this? Any enlightenment on this would be appreciated. Thanks!

The technicals:
Canon 5d2
Canon 24-105 L
5.00s at f/11, ISO 100

Marylynne Diggs noticed a similar look on one of Ken Smith's photos posted here, and it got me wondering about my photos. I can't recall having seen this happen before.
http://www.naturephotographers.net/imagecritique/ic.cgi?a=vp&pr=230725&CGISESSID=8b1e6e7b97c393396bf30488796c6bf1&u=20920&title_action=va

Here's the whole image, straight out of the camera. The crop above comes from the LLC. I forgot to mention previously that a circular polarizer was used.

Craig, this is the same effect as is seen in flying water drops.  It's caused by the shape oscillations of the bubble (or drop) and how the different shapes scatter different amounts of light.  Here's a discussion link.
http://www.naturephotographers.net/imagecritique/bbs.cgi?a=vm&mr=77480&CGISESSID=08b123bab93d61b644894dd2205fe535&u=28056

Wow Mark, that is fascinating, and well above my head, but good to know! Thank you for the explanation.