As far as I know, all HN posts get a "past" button, as soon as they are posted.

I believe that your earlier post doesn't have a "discuss" button because it's in [dead] status. Why it's [dead] I can't say. Your account doesn't seem to be shadow-banned since this post showed up. Maybe the domain of the link is banned (why that would be, I don't know). Or maybe the spam detector just fired a false positive for some totally random reason.

You might want to try emailing hn@ycombinator.com and inquire with the mods. Maybe they can help out.