OP here - yes, something didn't work with dup detection?, this one was submited days ago, before then one you linked and both ended up on the front page. Certainly not intentional.
I'm happy it was posted again because I missed the previous post and I happen to need this cheatsheet right now.
If it had no or few comments, the dupe won't be treated as a dupe after some period of time. Then your submission probably ended up in the second chance pool and we get this situation. It happens pretty often.