The nagative post count is starting to be a quite common thing.
I got into the MemberList and noticed that there are a lot of people that have negative post count.
Go to the middle of the MemberList and start moving pages. You'll notice them.
I actually think it's rather a bug than an intended thing that people do.
Double posting in topics and then getting all the posts deleted was one way.
A member deleting one of the topics he/she started used to be possible and gave the member a -1 to post count for each and every post in the topic, including the case when the post belonged to another member. Some members have deleted topics with hundreds of post in them and then asked why their stats looked strange. It has never been possible for members to delete poll topics.
This has never happened when a moderator/admin has removed a topic, then posters lost 1 post count only for the posts they made there, and this applied to the thread starter as well. I think some of the readme I created Aeons back specifically mentioned this.
This was a long time ago and I think I noticed some time ago that Valeriy changed so members could no longer freely change/delete posts once they reached a certain age. (Noticed that in a link topic where I could no longer edit the first post to include new links.)
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"A brilliant light can either illuminate or blind. How will you know which until you open your eyes?"