This is an odd one. Doesn't really have an in-game effect, but it does mess up my attempts to create supporting documents such as orbital animations:
Tau Ceti, two planets and one moon generated. The second planet has a diameter of 27000, mass of 8.6129 Earths. Its moon also has a diameter of 27000, with a mass of 9.044 Earths and an orbital distance of only 135,000km. The moon is bigger than the planet. This hoses the orbital mechanics to no end. For one, it's basically a binary planet.
When I eventually created a simulation in Universe Sandbox (though it automatically swapped the planet and moon based on mass), the two had an interesting very tight helical orbit with both bodies corkscrewing along the main orbit path. However, because of the proximity they essentially constitute a single mass unit which is double what the orbit was calculated with. So they wind up diving into a comet-like path, slingshotting around Tau Ceti, and then the lighter of the two gets flung off into space. After that, the remaining body settles into a stable but highly eccentric orbit.