Hi Denis,

Yup, I see the problem. The same thing happens to all non-round
planets; it's just most noticeable with Jupiter and Saturn (because
they're most flattened) and even more so with Phobos and Deimos and
similar objects (because they're extremely non-round).

I've got at least a vague idea how to fix it with Jupiter and
Saturn, and some thoughts on possibly fixing it for irregularly
shaped objects.

-- Bill