I remember that CFS2 (which uses 8 bit for all terrain textures) used to dislike replacement ground textures and crash.
That was the reason I added the Import and Merge buttons that appear under the main image. These let you merge your changed data into the "shell" of a default texture and bypass the problem. There is a bit in the Bmp2000 documentation about it.
The other option may be to pass the final image through Imagetool as this will presumably correctly set all the header data correct for terrain use. I never did find out what was the cause and haven`t looked for several years as 8 bit has (mostly) passed into history
