Unity renders weird 3D gridlines on Terrain

So I imported a greyscale raster image to L3DT, smoothed it out and exported as a 1025x1025x16b RAW heightmap. It looks perfectly fine both in L3DT and exported to a PNG. However, when I import this RAW into Unity, it doesn't look so great any more. More precisely, there are dotted/dashed grid lines visible as height bumps. This is what it looks like with Pixel Error tuned down to 1: I haven't been able to find even a mention of this problem, and I'm kind of lost. How can I get rid of this? Here's the heightmap used: http://speedy.sh/6ZBFv/canyontest5d1025.raw