Apparently, if you name a planet (maybe any object) something that starts with the letter 'F', it will bug out your game. That object and possible other objects will reverse their orbits.
I have reproduced this bug several times. I name a planet something that starts with 'F' and it goes the wrong direction around the star. In the above image, Comet 01's predicted path is in light red, counterclockwise around my star. After I place a planet and change its name to start with 'F', its actual path is reversed (the dark red path) along with planet F*'s path. Both objects show a predicted path counterclockwise, but they actually travel clockwise.