Nice catch. You got it faster than I did. When I set up the blanks to turn, I looked at the sheet and read that the upper barrel was the shorter of the two and then didn't bother to look at the lower barrel (Process of elimination say it has to be the longer one). I turned several pens prior to assemble only to find out that the lower barrel is supposed to be the shorter one. It was a very frustrating loss of a few nice blanks and tubes which are now trash.
I would contact customer service and see how they can take care of you.