I'm getting this strange secant in the orbits of seemingly all objects (planets and moons)... Is this normal or is there a bug?
Here are screenshots of what I'm seeing:
What's going on?
That indicates that you are using a Nvidia MX card. This is a bug on MX card that is up since several driver versions now. Try to set you 'number of orbit points' setting in 'celestia.cfg' to a lower number.