I have no inside knowledge, this is speculation based on close observation.
The main page ranking algorithm I believe tries to prevent flame wars, if over a short period of time a post gains more comments then up-votes (or some specific ratio) the post is penalised. IMHO this is good, it is a good indication of a "hot" topic that can get out of hand.
Although your post now has many more comments than up-votes, I am suspicious that it may have triggered this process earlier on.
Additionally, and again this is speculation, I think the mods sometimes add extra "gravity" to some domains (certainly twitter.com and reddit.com) and some key words. It may be that they have added gravity to any submission with "Reddit" in the title. This won't be to remove the discussion, but to ensure that the front page isn't just inundated with posts about Reddit rehashing the same discussion. They still make it onto the front page, just slightly more briefly, and the discussions are still happening.
If you take a look at the current "best comments" list, it's apparent just how engaged the community is in these threads: https://news.ycombinator.com/bestcomments
If you have any more concerns, Dang is very responsive to email (contact link at the bottom of the page)
