Replace a string in all posts

There must be something I’m not understanding here. I’m trying to replace occurrences of :THUMBS-UP: with :+1: across almost 3M posts (including PMs). I ran:
rake posts:remap[":THUMBS-UP:",":+1:"]
And after about 50 minutes of ................. it returned 40000 posts remapped! This seems like a suspiciously even number. I did find some occurrences that were replaced with :+1: in both recent posts and posts from many years ago, but there are also a ton of :THUMBS-UP: even in the same topic threads that also have some successful :+1: replacements.