"It's done by design. You either have to un-check the button on the post or just ignore the subscriptions."
Per Island Dog (Stardock) in the galciv thread. Kinda sucks as a design in my opinion. However, for some reason on JU, leaving that checkbox checked does not subscribe me to the thread. I reply a lot, ignore the checkbox, and currently have zero subscriptions. I have my profile set to not subscribe FWIW.