marcury
Thanks for sending that through.
The issue is that the parent of your other sphere (group2) is scaled -1 in x.
Ziva can't compute the volume of the second sphere properly because everything is inside out, is my guess.
When you do the mirror, if you look in the script editor, there is useful information there.
I'd suggest freezing transforms, deleting history and cleaning up any extra shape nodes on all geometry before applying Ziva nodes.
Lastly.. you've got kind of an unusual naming convention. It seems fine in this case, but just curious why your objects have a leading underscore? I'd expect it to look like r_ball_tissue, rather than _r_ball_tissue, for exmaple
Hope that helps!
Andy