Here’s a fix.
https://github.com/discourse/discourse/pull/23380
@Don thanks for your wonderful repro. I have attempted to repro it is failing successfully 
The problem with these embedded replies is that the reply_to_post_number is set to 1, when it shouldn’t be set.
I’m considering adding a migration to existing post voting topics to clear the number if it is set to 1, that prevents the embedding in older posts where that number is set. The downside to adding the migration is that forums may have more (post voting) posts show up now when they were originally embedded.