As the title says, the editor's grid texture is rendered mirrored on the top side of it alongside the base block being mirrored on the bottom side when compared to the custom grid texture.

Video showing that this is the case:
[CPMGridTextureIssue.mp4]https://github.com/user-attachments/assets/3abc5490-a6ca-44de-929e-5791a62dab96

The texture pack itself can be found here:
CPMGridTexture.zip

The planks texture used as the grid itself was taken from this mod's textures folder, scaled up and tiled to fill the grid area and added the arrow with the letter to match how blockbench does it for pointing towards the front.