I've noticed this too for quite some time, however, I've also noticed other oddities going on with the comments in general:
- As I said previously, I've noticed on some videos, a comment you posted will disappear if you're not logged in, or on another account, but will reappear when you're logged back into the account you posted the comment.
- As I also said previously, you apparently can't post links in comments anymore, not even to other videos; I supposed Google actually caught onto that one because people were intentionally posting sketchy links to show them at enabling that ability when they switched to the Google+ comment system was actually a bad idea.
- You can only click "load more comments" so many times on a video before it will stop loading altogether, particularly videos that have a large number of comments (like hundreds or thousands); it doesn't matter which you browse under, however, I've found that it loads fewer comments when browsing under "Newest First" as opposed to "Top Comments."
- Comments disappearing altogther. Though, I suppose that can be chalked up to people going back and deleting their comments, but it seems to be happening more and more frequently for seemingly no reason.
- This is one I had to do research on, because I couldn't figure it out: you can't space your comments by pressing enter alone, you have to press shift+enter to space your comments.
- Certain comments you can't reply to for some reason, even if they were posted after the Google+ merge took place.