There are no indent on first reply, and not on any later replies either, which makes it seem like all replies goes on the last except if you disagree on a previous post. You can then digress on the last reply without it ever showing up in the reply structure. This is confusing.
It would be better to always indent a reply, that is it will be clear who you make a reply to, even if you reply to the original post. That makes it a lot more obvious if you move back to the original post, because then you make a reply on the original post, not as now to digress on the post.