These lugs aren't reamed, the lip is intentional. The lip allows the builder to leave the top of the seat tube cut square. It's an advantage for some folks, mainly production builders. My fixture doesn't work that way, it has a cone at the top of the seat tube.
I have bored it out on my lathe on a couple of lugs. It always seems like an annoying task until I do it, but it's no big deal. IIRC, I have some Llewellyn lugs with a lip.
img_0045.jpg by
unterhausen, on Flickr