That is probably because of the way brick textures work in blockland and there is no way for me to fix it.
If a face is smaller than 1 TU and should have a side texture, the texture will actually be scaled down smaller than the face and then extruded so the borders are exactly 11/512 TU thick.
You'll need to modify every side material and set it to extrude instead of loop, as I can't store that info in a obj file.