Python утечка на полке?

Question

Похоже, что при перезаписи ключа на полке при определенных обстоятельствах размер полки неожиданно увеличивается. Это как если бы некоторые данные на полке не имели ссылки на них, как в случае утечки памяти. Похоже, это как-то связано с добавлением в списки. Кто-нибудь знает почему? Вот минимальный пример:

import shelve, os
import numpy as np

def run():
    list_array = []
    expected_size = 0
    for i in range(5):
        array_100mb = np.zeros(1024*1024*100//8)
        list_array.append(array_100mb)
        expected_size = 100*len(list_array)
        with shelve.open('shelve_test') as s:
            s['val'] = list_array
        size_mb = os.path.getsize('shelve_test.dat') // 1024 // 1024
        print(f'Iteration {i}: \t shelve size is {size_mb}Mb; \t expected size is     {expected_size}Mb')
        
for j in range(5):
    run()
    print()

Это выводит:

Iteration 0:     shelve size is 100Mb;   expected size is 100Mb
Iteration 1:     shelve size is 300Mb;   expected size is 200Mb
Iteration 2:     shelve size is 600Mb;   expected size is 300Mb
Iteration 3:     shelve size is 1000Mb;  expected size is 400Mb
Iteration 4:     shelve size is 1500Mb;  expected size is 500Mb

Iteration 0:     shelve size is 1500Mb;  expected size is 100Mb
Iteration 1:     shelve size is 1700Mb;  expected size is 200Mb
Iteration 2:     shelve size is 2000Mb;  expected size is 300Mb
Iteration 3:     shelve size is 2400Mb;  expected size is 400Mb
Iteration 4:     shelve size is 2900Mb;  expected size is 500Mb

Iteration 0:     shelve size is 2900Mb;  expected size is 100Mb
Iteration 1:     shelve size is 3100Mb;  expected size is 200Mb
Iteration 2:     shelve size is 3400Mb;  expected size is 300Mb
Iteration 3:     shelve size is 3800Mb;  expected size is 400Mb
Iteration 4:     shelve size is 4300Mb;  expected size is 500Mb

Iteration 0:     shelve size is 4300Mb;  expected size is 100Mb
Iteration 1:     shelve size is 4500Mb;  expected size is 200Mb
Iteration 2:     shelve size is 4800Mb;  expected size is 300Mb
Iteration 3:     shelve size is 5200Mb;  expected size is 400Mb
Iteration 4:     shelve size is 5700Mb;  expected size is 500Mb

Iteration 0:     shelve size is 5700Mb;  expected size is 100Mb
Iteration 1:     shelve size is 5900Mb;  expected size is 200Mb
Iteration 2:     shelve size is 6200Mb;  expected size is 300Mb
Iteration 3:     shelve size is 6600Mb;  expected size is 400Mb
Iteration 4:     shelve size is 7100Mb;  expected size is 500Mb

Python версия 3.6.6