Not Being Able to Reply More than Once
On threads, I used to be able to page down and respond to as many posts as I wanted. Now, I reply once and can no longer reply until I close out of the thread and come back to it. This is more of a problem with long threads because when you come back, the whole thread is collapsed and it's hard to find where you were and what you've already read. I just started noticing this recently.
This has already been brought up but I'm not going to link to it since it seems that nothing has been done. It's probably been a couple of weeks. VERY annoying. Not because of the replying more than once but, as you say, the fact that what would have been new replies are now thrown in the old mix.