Have you ever came across with the surface that is enable to unroll? How do you fix it?File attachedtake 5 - rails.3dm (718.9 KB)
Your surfaces will unroll if the narrow tips are split off and unrolled separately..
Many thanks @davidcockey for the explanation. D.LOFT tries to handle this problem by moving the final control points a tiny bit from their common tip, but that seems not to be sufficient in this case.