Problem with Sweep2(is it a bug?)

Recently I am modelling a bridge with Grasshopper, but a small problem comes up.
Check the files attached, open with Rhino and Grasshopper.
I used sweep2 for creating a structural component. In the green circle mark it works with one component, but in the orange mark, when it comes to multiple objects, it doesn't.
It's totally not logical. Is that a bug?
I've formerly met bugs with Sweep2 function(with circles), so I thought if this one is another bug with Sweep2 again?

Thanks for helping!