By texture you mean Texture Type = Default, rather than Texture Type = Sprite? That's what I'm doing right now, although I tried earlier with Sprites. I just tried a couple of smaller versions where each arrow was 64x64 and 16x16 respectively, but I'm still seeing the same problem.
Yeah, it seems to be reading one extra line of pixels from the next quad on the sheet. How does the asset decide where to draw the line between each quad?