Blocking a troublesome Plurker doesn't keep them from making friend's Plurks 'unread.'

I just blocked a spammer -- however, they weren't spamming me, they were spamming a friends Plurks via responses.

But, even though they're blocked, Plurk keeps telling me these topics have updated when the spammer posts in them... I don't want to unfollow my friends, but seeing all these Plurk 'unread' responses consisting of spam is annoying.