I don't know, Scott. You don't have any posts in the Recycle Bin (an admin place where posts go when you or a mod delete). I have a theory that periodic emptying of the Recycle Bin will reduce one's post count, but I can't say for sure and that wouldn't apply here anyhow. I'll bring this up to the Admins, see if we can figure it out.
No, for sure it's not when the recycling bin gets emptied out. When posts, or threads are deleted, they automatically go to a temporary recycling bin and just as automatically, the post number of their posters are also immediately reduced. It doesn't happen when the recycling bin gets emtied out.
Very few of the deleted posts/threads in Anything Goes have affected active members. If more than a post from an active member gets deleted, I try ta offer an option (like transfering it to their personal blog, or in the case of an image, I ask the poster if he/she's interested in repairing the post) in lieu of deletion.
Guess I'm not deleting as much as I might, but a lot a the dead threads/posts are from former members who have had their membership ta BetterMost discontinued (they show up as "guests").