Billboard editing

Hello all,

I'm trying to edit the billboards in the game, but am having difficulty.  I'll find the correct billboard texture in OpenIV, and import my own texture, but when I run the game, I'll only see my custom texture when I'm very close to the billboard itself.  If I'm too far away, a blurry image of the previous default texture will take its place.  How do I fix this?  Is there another texture file somewhere that contains a lower resolution image of the default texture that must be replaced as well?

Thanks.