Sweet orange peel tasting bitter?

I recently finished up an orange cream ale. I don't have the recipe on hand, but I added .5 oz of sweet orange peel (picked up from the homebrew shop) with 15 minutes left in the boil. After going through everything it's been about a month since it was bottled. I'm a little confused with the taste...it doesn't taste bad - great mouth feel, good hop character, everything - but the orange peel almost seems to have added a bitter taste/smell to it. I'm just wondering why using sweet orange peel added this character to it. Any ideas?

Orange peel, whether "sweet" or not will naturally have some bitter characteristics to it because of the natural rind of an orange on the backside of the skin. But the sweet stuff shouldnt be nearly as bitter as the "bitter" peel, obviously. I just kegged a belgian wit with sweet peel and grains of paradise without any bitterness attributed to the peel. 15 minutes is a long time, try 7 to 10 just to extract the flavor. Boiling anything too long extracts lots of bitter flavors. Think of tea, if you steep it for 10 minutes it will be really bitter, but 4 minutes makes a nice balanced cup, the same rule applies with beer additives.