It could be any number of things. The possibility of it being a stem that did not originally belong to the pipe is there. I definitely agree with uperepik about the stem being sanded down. The rounded edges of where the stem should meet the shank make it obvious. The stem not meeting the shank flush could be because of the briar drying out, heat, fiddling with the stem to much, gunk and tar build up, etc. Or it might be mismatched. I couldn't say for sure. Personally, I would leave it alone. Let someone buy it. I'm extremely picky with pipes though. It does have some beautiful grain.