addtiledef problems

[Yen]

Versus is having a tileset problem.
We have about 8 different tilesets for different areas.
When we log on, only one tileset is loaded, and it's applied to every level.
There's nothing setting this tileset. The only place addtiledef is used is in a System NPC that sets the tilesets for each level. I've debugged it and made sure it's setting the right tilesets in the right levels.
I've tried multiple ways of setting the tilesets; setting every tileset when the player enters a level, setting them all in the Control NPC, reseting the tiledefs when the player enters the level, and so on. None of them work.
Even removetiledefs() doesn't reset the tileset to default.
Nothing was changed in levels or NPCs, it just randomly happened one day.

Is there any known cause or fix for this?