This is not a new bug. I had hoped your upgrade would fix it, but apparantly it didn't. I generally use the "threaded" as opposed to the "flat" view to look at threads. Most of the time it works correctly, but a few threads seem to get "stuck." At some point, new messages posted to those threads will not show up in the threaded view. The only way for me to see those new posts is to view the thread in flat mode. Once this happens, I have found no way to get the thread "un-stuck," though it doesn't affect any other threads.
For example, right now the Bugs and Comments page shows 12 replies and one unread reply in the "Format with Netscape Navigator" thread. When I click on that thread, I see only eight replies, the last of which was posted at 4:05 pm yesterday. When I click on the flat view type, I see all replies through to the present. As more posts are added to this thread, I will only see them if I choose flat mode. Meanwhile, (almost) all the other threads are behaving normally for me.