That was my first thought as well! But I also tried LW which is still on 0.19.3, same problem.
Edit: My bad! I had "show read posts" enabled on my LW account, and read posts are correctly hidden when I disable it. So it really seems to be a problem with the new version.
If you use your lemm.ee account, it doesn't matter which instance you visit in Boost. It is always tied to the functionality of your account's instance.