.stack() or .facet_adjacency_matrix() error in Polyhedron

[jipilab]

The following Error happens in Sage8.9.beta8:

sage: s = polytopes.simplex(7)
sage: f = s.faces(3)[0]
sage: sf = s.stack(f)
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-3-fae09a40457d> in <module>()
----> 1 sf = s.stack(f)

/home/jplabbe/sage/local/lib/python3.7/site-packages/sage/geometry/polyhedron/base.py in stack(self, face, position)
   4135         neighboring_facets = set()
   4136         for facet in face_star:
-> 4137             for neighbor_facet in facet.neighbors():
   4138                 if neighbor_facet not in face_star:
   4139                     neighboring_facets.add(neighbor_facet)

/home/jplabbe/sage/local/lib/python3.7/site-packages/sage/geometry/polyhedron/representation.py in neighbors(self)
    463         adjacency_matrix = self.polyhedron().facet_adjacency_matrix()
    464         for x in self.polyhedron().Hrep_generator():
--> 465             if adjacency_matrix[self.index(), x.index()] == 1:
    466                 yield x
    467 

/home/jplabbe/sage/local/lib/python3.7/site-packages/sage/matrix/matrix0.pyx in sage.matrix.matrix0.Matrix.__getitem__ (build/cythonized/sage/matrix/matrix0.c:7282)()
    963                     col += ncols
    964                 if col < 0 or col >= ncols:
--> 965                     raise IndexError("matrix index out of range")
    966                 single_col = 1
    967 

IndexError: matrix index out of range