I've noticed that when it's the equinox on this planet I'm making, the sun seems to cast a double shadow on the planet. How come the planet's ring seems to make two shadows with a space in between, instead of one "line" shadow. Is this accurate to real life, or a quirk of the rendering engine I'm using?
This might happen if you model the ring as opaque but of very little thickness and in the same plane as the vector between the planet and the sun Seen edge on from the equator, the ring would block none of the sun's light, but from a little north or south of the equator, the ring would block more of one hemisphere of the sun.
So I would check first if your geometry has things lined up too perfectly before considering a fault in the rendering engine.
The shadow cast by the rings onto Saturn is much more pronounced as shown by the Cassini spacecraft (e.g. here). Mind also, that the shadow is comparatively sharper than on Earth as the sun's apparent diameter is smaller at the ring planets' distance.
And, of course, the intensity of the shadow depends on the density of the rings - and the obliquity of the rings wrt light direction; they are extremely thin, and not very much packed with material, yet when you look through them nearly radially, they still block most if not all light.