Latest version stops supporting mesh refinement with periodic boundaries?

I recently updated my Ubuntu system and also updated the version of ngsolve to 6.2.2406. However, the following codes, which worked before in refining a mesh constructed from a geometry with periodic boundary conditions, now die at the step mesh.Refine(). It will show a malloc(): invalid next size (unsorted) or double free or corruption (out) error. See the attached file
debug.py (703 Bytes).

from ngsolve import *
from netgen.occ import *

sidelength = 1

cube = Box(Pnt(0,0,0), Pnt(sidelength,sidelength,sidelength))
cube.faces.Min(X).name=“back”
cube.faces.Max(X).name=“front”
cube.faces.Min(Y).name=“left”
cube.faces.Max(Y).name=“right”
cube.faces.Min(Z).name=“bot”
cube.faces.Max(Z).name=“top”

cube.faces[“back”][0].Identify(cube.faces[“front”][0], “bf”)
cube.faces[“left”][0].Identify(cube.faces[“right”][0], “lr”)

geo = OCCGeometry(cube)
mesh = Mesh(geo.GenerateMesh(maxh=0.5*sidelength))

mesh.Refine()