[ASK]Using no-follw tag on purpose?

Ok, I've had an attack of Scrapebox commenting on my blog and I've noticed that sometimes the poster deliberately puts the no-follw tag in the backlink. My blog is not no-follw, and all comments get moderated, so the comments are never posted.

Anyone know why they are doing this?

they try to look legit...no-follow links are still useful!

He believes it will benefit him, or wants to find out if it will benefit him

I doubt he is doing it to keep himself of askismet's radar.