Undocumented behavior when setting the fulfillment availability for listings at multiple sources

[lucas-sunco]

Observed behavior:
The quantity for the DEFAULT fulfillment channel is not immediately updated, and it cannot be set to 0.

Reasoning:
Using our API (leveraged by python-amazon-sp-api), we can fetch fulfillment availability for individual listings:

In [5]: api.get_listing_details(sku=sku)
   ...: 
Out[5]: 
({'list_price': Money('14.99', 'USD'),
  'business_price': None,
  'fulfillment_availability': [{'fulfillmentChannelCode': 'DEFAULT',
    'quantity': 143},
   {'fulfillmentChannelCode': 'aaaa-bbbb-cccc-dddd-eeee',
    'quantity': 66},
   {'fulfillmentChannelCode': 'ffff-gggg-hhhh-iiii-jjjj',
    'quantity': 77}],
  'sku': 'ASDF-ABCD-12PK-FBM',
  'status': 'BUYABLE, DISCOVERABLE',
  'asin': 'B0XXYYZZVV',
  'sale_price': None,
  'sale_start_date': None,
  'sale_end_date': None,
  'your_price': Money('14.99', 'USD')},
 datetime.datetime(2024, 11, 1, 13, 1, 59, 59595, tzinfo=datetime.timezone.utc))

We can also update availability for multiple channels using listings_items.patch_listings_item:

In [6]: 
   ...: fulfillment_availability = [
   ...:     {
   ...:         "fulfillment_channel_code": "aaaa-bbbb-cccc-dddd-eeee",
   ...:         "quantity": 1,
   ...:     },
   ...:     {
   ...:         "fulfillment_channel_code": "ffff-gggg-hhhh-iiii-jjjj",
   ...:         "quantity": 2,
   ...:     },
   ...:     {
   ...:         "fulfillment_channel_code": "DEFAULT",
   ...:         "quantity": 0,
   ...:     },
   ...: ]
   ...: 

In [7]: 
   ...: data = {
   ...:     "body": {
   ...:         "productType": "PRODUCT",
   ...:         "patches": [
   ...:             {
   ...:                 "path": "/attributes/fulfillment_availability",
   ...:                 "op": "replace",
   ...:                 "value": fulfillment_availability,
   ...:             }
   ...:         ],
   ...:     }
   ...: }

In [8]: 
   ...: response = api.listings_items.patch_listings_item(
   ...:     sellerId=seller_id,
   ...:     sku=sku,
   ...:     **data,
   ...: )

In [9]: response.payload
   ...: 
Out[9]: 
{'sku': 'ASDF-ABCD-12PK-FBM',
 'status': 'ACCEPTED',
 'submissionId': 'fb76ba785cbe4d37a7879e851caasdf',
 'issues': []}

As one can see above, the quantity for DEFAULT channel is set to 0, as required by the documentation.

However, that's not reflected within the listing updated data:

In [10]: api.get_listing_details(sku=sku)
    ...: 
Out[10]: 
({'list_price': Money('14.99', 'USD'),
  'business_price': None,
  'fulfillment_availability': [{'fulfillmentChannelCode': 'DEFAULT',
    'quantity': 143},
   {'fulfillmentChannelCode': 'aaaa-bbbb-cccc-dddd-eeee',
    'quantity': 1},
   {'fulfillmentChannelCode': 'ffff-gggg-hhhh-iiii-jjjj',
    'quantity': 2}],
  'sku': 'ASDF-ABCD-12PK-FBM',
  'status': 'BUYABLE, DISCOVERABLE',
  'asin': 'B0XXYYZZVV',
  'sale_price': None,
  'sale_start_date': None,
  'sale_end_date': None,
  'your_price': Money('14.99', 'USD')},
 datetime.datetime(2024, 11, 1, 13, 2, 49, 302856, tzinfo=datetime.timezone.utc))

After 0.5~1 minute it gets automatically updated to the net quantity from combined channels:

In [11]: api.get_listing_details(sku=sku)
    ...: 
Out[11]: 
({'list_price': Money('14.99', 'USD'),
  'business_price': None,
  'fulfillment_availability': [{'fulfillmentChannelCode': 'DEFAULT',
    'quantity': 3},
   {'fulfillmentChannelCode': 'aaaa-bbbb-cccc-dddd-eeee',
    'quantity': 1},
   {'fulfillmentChannelCode': 'ffff-gggg-hhhh-iiii-jjjj',
    'quantity': 2}],
  'sku': 'ASDF-ABCD-12PK-FBM',
  'status': 'BUYABLE, DISCOVERABLE',
  'asin': 'B0XXYYZZVV',
  'sale_price': None,
  'sale_start_date': None,
  'sale_end_date': None,
  'your_price': Money('14.99', 'USD')},
 datetime.datetime(2024, 11, 1, 13, 2, 49, 302856, tzinfo=datetime.timezone.utc))

For further context, this is the payload for the API listings_item.patch_listings_item method:

{
 "body": {
       "productType": "PRODUCT",
       "patches": [
           {
               "path": "/attributes/fulfillment_availability",
               "op": "replace",
               "value": fulfillment_availability,
           }
       ],
   }
}

As observed, the operation replace is being used.

Is that an expected behavior?
Is it possible there was update to API not reflected in the documentation?
Am I referencing an accurate version for the MLI Integration Guide?