When replying to a post using the reply function at the bottom of the post, this will repeat the post you're replying to. However...

Post your own additions AFTER the [\quote] sign, otherwise your addition will become indistinguishable from the post you're responding to...

Sometimes, you'll have to scroll down a bit to find it, but it will be there, I promise..

Better still, use the NEW REPLY function, which doesn't double the previous post and it will normally be quite clear what you're responding to.