Fun with tiledefs!

[Yen]

I have a system which loads the tilesets at log on.
However, two levels revert to the previous tileset when you enter.. And then back to the new tileset when you leave them.

I tried setting the tileset when you enter the level. It didn't work.
I looked through the level (as text) for any tile-modifying scripts. Nothing.
I cleared the level's NPCs, incase a putnpc2 was doing it. Nothing.

Any ideas?