This is just something I discovered and not a bug.
There is a five level nesting limit to replies.
After the fifth nested reply, there isn't a reply link on the last post.
What you do then, is reply to the post just above that post.
There will be a pop-up box. Someone mentioned elsewhere that they were getting a half box that wasn't scrollable for some other issue.
That is exactly how the box looks. HOWEVER, if you type to the end of the box, when you run out of room, the scroll bar appears and you can type as much as you like ... well, I didn't actually try out HOW much you can type, but it is more than the initial space displayed.
Sorry, this is a long post, but if you scroll down of do a page find on NESTING LEVEL LIMIT ???? you'll see what I mean.
The post appears after the post lacking the reply link.
Then again, perhaps I should not have posted this FYI. It might discourage people who discuss a topic to death, arguing endlessly the same thing they have already stated numerous times in the same thread. If they don't see a reply link, they might think they can't.