green spots in my carrot muffins

I made a batch of carrot muffins this weekend. They were fine when they came out of the oven. I ate a couple after they had cooled somewhat and they tasted fine. Later, after they had cooled completely, I noticed that there were little green spots dotting the exterior and the interior of the muffins. It turns out the some of the shredded carrots had turned green. I noticed this while I was eating one later and, again, they tasted the same.

Has this happened to anyone? Did some sort of (benign) chemical reaction occur? The recipe wasn't unusual--flour, oil, sugar, baking soda, vanilla, carrots, buttermilk, eggs...

Thanks.