Clearly, either code was "stepped on" or code was changed that interferes with accurate reporting of deletions from self-moderated threads.
I'm not exactly clear on what you mean by
stepped on, but I'm assuming that means changed by Theymos or someone with admin privileges. If that's the case, could they have made it any more confusing? Why not make it obvious what's meant?
It's a bug.
Hopefully it is that and not just Theymos making the meaning of things even more obscure than they already are--and if you need examples of that, just take a look at some of the forum rules, the trust system, and probably a few other aspects of the forum as well.
I remember back when cryptohunter was trolling the forum there used to be a way to tell how many posts had been deleted in self-moderated threads, but I don't remember the display looking anything like what OP showed. Did that change?
Edit: Oh crap, I missed Theymos's post right above me. Thanks for clarifying that, boss of bosses.