I don't know if this is a bug or a feature

but if I put a void in the middle of an object, then S3D slicer fills it in. I've been trying to make a rattle which while printing I can drop in some rice or some other objects and then when printing is finished the rice is completely enclosed in the object I'm printing. But no luck... I've tried a lot of options (and yes, "Merge all outlines" is unchecked), but no go. Whenever and wherever there is a completely enclosed void, S3d fills it in.
Anyone know if its possible to have the S3D slicer respect the internal voids, giving them outlines and appropriate top and bottom solid layers?