Well, I just made hobbit.world and intend to only have Tolkien related communities there. So block away if that’s not your thing. However, the only way to block an instance is to defederate and that’s kind of harsh. Hopefully the feature of blocking communities by instance is added.
I have the same problem even after unchecking read posts. Of course, it’s a bug either way. In the meantime I just always click the save post button so my posts show up there instead.