"Comment on" on displays underneath only the topmost node that you can see. Then the nodes below it (its replies) get "reply" next to them. But if you pick one of those and click on it, so that it becomes the top level node (from your pov) it will again display "comment one", and the "reply" button will disappear. Having a "comment on" underneath each node would get annoying.

Dont worry, youll get used to it.

:-)

--- demerphq
my friends call me, usually because I'm late....