I'm looking through the spritesheets and do not see anything that you're describing. Can you provide a screenshot? The only thing I can think of are reflections that are drawn on the cockpit to give a reflection/light source.
Mine doesn't look like this at all. This might be something to do with the engine you're using. I've ran into similar issues when I've done some game dev with sprites - typically something with rendering sizes because if you look at the sprites in your own screenshots the pixels are all different sizes themselves. But I went through every spritesheet and didn't see anything like this that you've shown.
