Sorry Todd for the long delay.
After some investigation I found out this is technical limitation of
illustration drawing.
As illustration creates illustration line in 3D space it has "width" in
physical 3D space.
In this model, the distance between two object is shorter than the
width of illustration and it sticks out. Some sort of extreme case.
The only workaround would be adjusting objects very tiny bit. Or use another view.
That probably isn't what you wanted hear but I hope it helps you understand whats happening.
Regards,
Kelvin