A possible case, if you look at this post https://steemit.com/rickandmorty/@cryplectibles/don-t-even-trip-road-trip-or-i-m-rickmobile-riiiiick#@robertsekhose/re-cryplectibles-don-t-even-trip-road-trip-or-i-m-rickmobile-riiiiick-20170927t173032760z the commenter @robertsekhose left the comment and upvoted the post.
Today two people found that persons comment upworthy (I can't judge that), they do not upvote that post, I check out https://steemit.com/@robertsekhose/comments and notice some decent payout one word comments being upvoted by the same user. All I can see is this person with no posts is banking on these comments all over, which I would have never noticed if they didn't do it on one of my posts.
Yes, the late-upvotes on random comments scheme is getting more popular. They sometimes even pick inactive accounts specifically to post comments under months old posts for that same purpose of not being seen pumping their rewards in this way.
Thanks for the lead, I've filed it in my backlog and will check on the suspect when I find the time!