Texture changes don't work on "Notebook Paper" texture in Battlemaps Classic

If you try to change the scale, rotation, or offset of the Notebook Paper texture (which is the default texture when you create a map in Battlemaps Classic), it doesn’t change. As soon as you move focus away from the sliders, it reverts back to its original size.

I made a custom sized map (50×40), and I want the Notebook Paper texture to match the grid, i.e. 50 columns, 40 rows, but I can’t do that.