Lofts: Joined and Unjoined produce different density



This is an enlightenment and edification question. I am wondering why I get two different results here.

Here I have a set of pairs of lines and curves in a hull form. The curves and lines are all G1. The curves have all had rebuildcrvnonuniform run on them.

Here I have lofted the lines and the curves separately then joined them. This gives the result I expected.

Here I have joined the curves and the lines then lofted them.

I am curious why the joined version results in such density while the unjoined then joined version does not.