Very weird that this isn't the case.
oh yeah this is a weird one, personally I think of block as "stop this person from contacting me", I suppose because I think of blocking phone numbers as the original definition of block. I don't put too much value in "don't show this person I exist" because it's not immune to new accounts or logged-off use. At the very least this distinction could be communicated better. Maybe if you click block, pop up a confirmation dialogue:
Are you sure?
This person will no longer see your posts or comments.
(checkbox) Also don't show me their posts or comments.