Ok, here is a fix I like. It uses the Reorient_Trans() macro which seems
to reorient it in a logical way (ie the cone doesn't rotate oddly). It
requires an #include "transforms.inc" in shapes.inc, but that's shouldn't be
a problem.

#macro Supercone(PtA, A, B, PtB, C, D)
   intersection {
      quartic {
         <0, 0,  0,  0,  0,  0,  0,  B*B-2*B*D+D*D, 2*(B*D-B*B), B*B,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0, A*A-2*A*C+C*C, 2*(A*C-A*A), A*A, 0,  0,  0,  0,
         -(A*A-2*A*C+C*C)*(B*B-2*B*D+D*D),
         -(2*((B*D-B*B)*(A*A-2*A*C+C*C)+(A*C-A*A)*(B*B-2*B*D+D*D))),
         -(B*B*(A*A-2*A*C+C*C)+4*(A*C-A*A)*(B*D-B*B)+A*A*(B*B-2*B*D+D*D)),
         -(2*(B*B*(A*C-A*A)+A*A*(B*D-B*B))), -A*A*B*B>
         sturm
      }
      cylinder {0, z, max(max(abs(A), abs(B)), max(abs(C), abs(D)))}
      
      bounded_by {cone {0, max(abs(A), abs(B)), z, max(abs(C), abs(D))}}
      
      #local Dirv = PtB - PtA;
      scale <1,1,vlength(Dirv)>
      #local Dirv = vnormalize(Dirv);
      #if(vlength(Dirv-<0,0,-1>)=0) scale <1,1,-1>
      #else Reorient_Trans(z, Dirv)
      #end
   }
#end


-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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