Is this only happening on my board? Is there a quick code fix for this?

Can someone please help me out?

This has become a very serious problem on my board. The admin log shows only deleted posts... but NOT deleted threads.

You can add this to doexpirethreads, down towards the bottom, right before the $html -> send_header() line;

require("admin/admin.inc.php");
admin_log("DELETETHREAD", "{$user['U_Username']}:$Keyword:$Number");

Many thanks, Rick. Just tried it out and it works perfectly.