Simple answer is the tiles to support corridors and doors in the same way as the standard NWN tilesets just aren't there. Its understandable in a way because the sheer number of tiles required to make that kind of functionality is huge - I started my "some interior" tileset almost two years ago and have only been slowly picking away at it ever since. It's still not quite finished.
Badwater wrote...
(like the Haunted tileset)?
If you're looking to use the Haunted Interior tiles, I'd reccomend using the standalone version Worms posted on one of his other vault pages. That has quite a lot of functionality (including a seperate set of corridors and working doors) that he apparently forgot to include in the Fantasy Interiors version. To be honest, the latter set seems like a rather rushed piece of work to me, as there's not really much in there that isn't just quick reskins and edits of his earlier work.
I mean, c'mon - all I wanted was a Pepsi.
Suicidal Tendencies or Cypress Hill?