Wow, I've had this problem for YEARS -- in fact I was looking to hire a coder to create a cron job to reset all these posts counts to zero. But I've had to manually reset these post counts counts for 4 or more years. I complained about it here a long time ago.
This has been a plague that I ALWAYS thought was caused by PP Classifieds but only just recently proved it on my website.
I didn't have the exact same original coding as Chuck S. detailed in his fix. I had the following at line 620 of adm-misc.php:
Content visible to verified customers only.
I changed my coding as shown above. I'm hoping and praying that his has fixed the issue.
I'm tired of having to fix all these posts counts every week. Earlier this year I forgot to deal with this issue for a couple of months and I had over 150 members with post counts of 4,294,967,295 and I had to manually go through and fix each of them.