scipy.sparse.csgraph.maximum_bipartite_matching is broken when get complete bipartite graph

test.py

from scipy.sparse import lil_matrix, csr_matrix
from scipy.sparse.csgraph import maximum_bipartite_matching
import random

N = 10
M = 10
random.seed(0)
for x in range(5):
    mat = lil_matrix((N, M))

    for i in range(N):
        for j in range(M):
            w = random.randint(0, 100)
            mat[i, j] = w

    mat = csr_matrix(mat)
    # solve
    print(maximum_bipartite_matching(mat))