I noticed those marks on my first experiment, but not the second or third. The only change from the first to second attempt was going from 0.08" thick tabs to 0.05" so that the tab would be completely trimmed with the 1/16" round over. I ended up concluding that I made those marks with the chisel when I cut the tabs, but now that you mention them, my conclusion is likely wrong. But I can't explain why I didn't get those marks on runs 2 & 3.
In my particular case, the tab is completely removed with the round over I was doing anyway.