hi there

that's got something to do with the bottom seam (may be michael will hop in with an explanation, i really can't remember) ..so a workaround would be

1 separate the object into faces
2 rotate the bottom surface just a bit
3 join to make solid
4 select edges ( are a bit cluttered now)
5 chamfer

but to be honest..just rebuild the ring like bemfarmer suggested.







~ marco