Joined Curves dont smooth between each other

 From:  nukkle
hi i ve here 3 curves

curve C1 is a outline of a surface
curve C2 is a drawn curve
curve c3 is a drawn curve

1.i tried to join c1 and c2. joining is succesfull, but one problem stays. the point between c1 and c2 where the curves are melted wont be smoothed. why?

2. i tried to extend c1 to c3. but it doesnt work. why?

is there something special about c1?

kind regards