Help BiArc command

Hi,

I'm a new user of grasshopper and I have to convert a spline in tangent arcs and I did it thanks to the biarc component as it was explained in other discussions of this website. But I have a problem, somebody told me that the biarc split goes out of plane where it changes, but i don't know what does it mean also because if i generate the plane of each arch it seems to be correct.

Need your help please