I am currently learning how to do UV unwrapping in Blender. I have been making PNG -24 files in Photoshop that have transparency, but I get annoying white edges (marked:)
Photoshop does apparently have problems with PNG transparencies from my research.
It was strange, all layers in the original were cleaned so there was no pixels in Photoshop. I read that there was a setting on export that disables the matte but on investigation could not be set (it was greyed out for me). I then remembered that I saw the above option for matte removal and the problem appeared to go.