Replying To A Newsgroup Message ?

[Bob]

Hello,

New user.

Using only for my newsgroup access, via Motzarella/eternal-september.
Not for e-mails.

I open up a message, and wish to reply to that message.

However, even as I do as a REPLY, when the original Post is opened up,
it seems to start a new topic with my reply, rather than putting it
under the original message.

Why ?

What might I be doing incorrectly ?

Thanks,
Bob