Orbits are only shown for planets, not brown dwarves or stars, though trails can be shown for anything.
In Alpha 18.2c, it appears that, randomly, gigantic orbits are generated that flash and flicker, and appear to be attempting to depict a spurious orbit of stellar bodies.
To re-create this bug, construct a star system with a binary or trinary sun, then add a number of other stars as "neighboring stars", e.g, Sun, Alpha Centauri, Spica, Antaries, all within a few tens or hundreds of light-years of the initially created system.
In addition, there seems to be corruption of the "grid" as well.