error when re-loading mesh from file

The error is this. If I create a 3-D mesh from scratch, with some uniform refinements, it has a certain number of faces, facets, and edges. I then save the mesh to a .vol file. When I reload the mesh, the number of faces, facets, and edges is different. Why?

I have created a sample code below.

import numpy as np

import netgen.gui
from ngsolve import *

from netgen.csg import unit_cube
from netgen.csg import CSGeometry
from netgen.csg import Pnt
from netgen.csg import OrthoBrick

#load_mesh = True
load_mesh = False

mesh_FN = “test_mesh.vol”

if load_mesh:
print(“Load mesh from file.”)
mesh = Mesh(mesh_FN)
print(“Create mesh from scratch.”)
# make the mesh
cube = OrthoBrick( Pnt(0,0,0), Pnt(1,1,1) ).bc(“Gamma”)
geo = CSGeometry()
mesh = Mesh(geo.GenerateMesh(maxh=1.0))
for r in range(3):
# save the mesh

print(“Some info about the mesh:”)
print("Number of Elements: " + str(
print("Number of Faces: " + str(mesh.nface))
print("Number of Facets: " + str(mesh.nfacet))
print("Number of Edges: " + str(mesh.nedge))
print("Number of Vertices: " + str(mesh.nv))

When you run it the first time, you should get:

From scratch:
Number of Elements: 3072
Number of Faces: 7530
Number of Facets: 7530
Number of Edges: 4905
Number of Vertices: 729

Next, change “load_mesh” to True and rerun. The output will be:

When loading from file:
Number of Elements: 3072
Number of Faces: 6528
Number of Facets: 6528
Number of Edges: 4184
Number of Vertices: 729

Why is it different?