cylinder model rebuilt with delaunay triangulation and freeboundary

I got a 3D stl cylinder model,I import the stl file into matlab,and got a matrix p of all the coordinates of the model vertex.After I use delaunay triangulation and freeboundary,I the top and bottom face of the model has changed. Here is my code and the comperion of two models(attention to the top and bottom face).

[p,t,tnorm]=STL_Import('prt0004.stl',1);
TR=triangulation(t,p);
trimesh(TR);
DT = delaunayTriangulation(p);        %retriangulate all the points and create their connectivity
[tri Xb] = freeBoundary(DT);
 TR2=triangulation(tri,Xb);
 trisurf(tri,Xb(:,1),Xb(:,2),Xb(:,3),'FaceColor', 'cyan', 'faceAlpha', 0.8);

[LIN Hongbin]

Warning: Duplicate data points have been detected and removed. The Triangulation indices are defined with respect to the unique set of points in delaunayTriangulation property X.

[LIN Hongbin]

How to solve this warming,when using delaunay triangulation