Does a chain ever need to be loosened by bending sideways with Shimano reinforced pins?
I've certainly had a stiff link at the join on my 8-speed hybrid. I usually use IG51 on that, but have used HG71 so I can't remember which one gave the stiff link. Since using master link chains on my newer bikes I've started to prefer them, but could only get HG53 recently, with a special pin. That didn't stick, but like you I was half expecting it to.