Ring marker woes

I can't believe I've done this TWICE! I've somehow managed to get my yarn knit "through" my closed-ring marker. I thought I was careless the first time around. Now I've discovered that I've done it AGAIN! And this time I was very careful too. How did this happen?

I'm working on the Flower Basket Shawl and have a closed-ring marker before and after the Center Stitch. There is a YO before the first marker and a YO after the second marker. So it looks like this: YO - Marker - Center Stitch - Marker - YO. I suspect that there's something about those YOs that caused the yarn to go THROUGH the Marker while I was knitting the next row above (purl across). I just can't figure how it happened though. :( Any ideas?

You can see two strands of yarn going through the ring marker on the right side.