Are you sure you're saving your image as a transparent one? Also as a .png for that matter. Make sure that you're not drawing over the transparent part of the mane. Also try erasing the mane texture that is multiplied onto the transparent areas.
Not sure if this is a transparency problem, but it might be helpful to consider this.
Indeed transparency has nothing to do with this. I have tried to make presets and such have come out blocky what I have done to solve this somewhat is use a different mane texture then the game provides this may take some time to find ones that you will like or actually find -any- period. If all fails my idea is to try and make your own mane texture.
If the mane texture idea fails then please consider to change the .joh,.png,.tif, to whatever you are using that comes out as such.
If this had not helped please tell me. If it has asked someone to lock this.