A typo in MA_TextureUtils.cs on line 44 causes the copied texture to be the wrong size if the height is different from the width, this is the second time I had to fix this myself as updating it to the latest version still includes this exact same typo.

Texture2D myTexture2D = new Texture2D(texture.width, texture.width);
should be:
Texture2D myTexture2D = new Texture2D(texture.width, texture.height);

Please test your tool before uploading/updating it!!!

Also a suggestion: the exporting of the textures happens to one single folder, would be nice if you get a prompt to select where you want to save the textures, or maybe even have the path in the export settings.