When viewing a post normally, "Reply to this" and "Parent" links are displayed at the bottom. This is fine; both are useful. But when replying to a comment, only one of these is useful, and only one is displayed. However, the one displayed is the "Reply to This" button, which is entirely useless because you're _already_ replying to it! The "Parent" button, which would be useful to review post further up the thread, is missing (requiring to first re-open the _same_ comment in a separate window or tab, and _then_ click its "Parent" link.
On a related note, the "Hide Replies" link is shown as well. This, too, is useless, because other replies are not shown anyway.
Please change the "Reply to This" link to a "Parent" link, and get rid of the "Hide Replies" link, on reply pages. Thanks.
Incidentally, this bug has annoyed me for years; Slashdot's recent "What's the worst technical feature you've used" finally inspired me to post a bug about it. : )