Modding Planet, heightmap data ignored.

First real mod attempt and I'm stuck on getting my heightmaps to be accepted by ME. Per the help pages, using Photoshop I've created 6 2048x2048 resolution 16 bit greyscale .png files labelled front, back, left, right, up, and down. When a world is loaded with the mod, the materials maps (6 other 8bit .pngs) have been correctly changed, but the entire planet loads in as a smooth ball.

Edit: Turns out if you delete the old layer instead of flattening the image Photoshop saves the file as type 'GreyscaleAlpha'. Flattening the images before saving corrects this.