Don't know if this helps at all, but I found a few pages that were indexed with 1.8.0 and weren't with 1.8.1. These are all from
www.napathon.net
/AlbumID1107.php - which can be found on: /Rock12.php
/AlbumID1113.php - on /Rock23.php
/AlbumID1114.php & /AlbumID1115.php - on /Rock28.php
Doesn't make sense why these pages wouldn't be spidered. I don't have a complete spider log or anything, but I could go spider again and make that if you need it.