B.M.
Yep, normal. I remember when I was first babysitting (probably about 13 or 14) and I was changing the baby's diaper and saw what appeared to be the end of a balloon in the diaper and FREAKED OUT . . . . it was corn. I will never forget that (he's a sophmore at Purdue now! Wouldn't he be mortified to hear that story!).
Yes, there are certain things that go undigested and its not an issue with nutrition. His body is getting the good stuff.
More crazy info . . .it happens to you too! :-)
B.