I could have fixed this by adjusting the dungeon_feature_type enumeration to place special walls earlier, but I'm a little scared of mucking with it.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5371 c06c8d41-db1a-0410-9941-cceddc491573
QMA3SGVILLTLUXDRKS6X7FZSN7VZZKU3UMV5FOJ7ENEEME23U4GQC