Funny Vector Blend Effect

I was just playing the other day, recreating this tutorial, glassy button and mixing my own colors ...



and changing some elements, trying to create some different effect...



and all of a sudden, when I tried to use blending on these next two objects, while one of them is spiral lines, this funny and strange effect happened.


Left image is before blending, right image after. I can understand extra spirals, but what's that new line all about? Interesting however, can be used as random shape generator or something.