Comments with a positive pending payout will be shown no matter how low reputation score the author has. Now bots adopted simple strategy: self-upvote after posted a comment. See https://steemd.com/@backetri for example.
It's by design, but I think it's a bug.
//Update:
I'm now using the @adm account to manually downvote found spamming replies. Wish the issue get fixed sooner.