Well actually it does because you're wrong about this, it isn't about him replying to you, he manually sets a flag on your account.
Right, but in my experience, this usually occurs after a reply.
Not going to keep replying, as I suspect that a conversation between two people flagged in this manner is one of the likeliest to turn flame-y :)
Wait, I'm now wondering if I've been limited. I've never once seen the "Vouch" button and I've flagged some blatant stuff that nothing happened to, but figured there was somewhat of a vote (or multiple flags) before it took any effect. Can anyone confirm this behavior?