Reload is not working when the field name is "items"

Here is the data model where reload works

class TestDoc(Document):
    item = IntField()
t_d = TestDoc()
t_d.item = 1
t_d.save()
TestDoc.objects(id=t_d.id).update(inc__item = 10)
t_d.to_json()
t_d.reload()
t_d.to_json()

Results in

'{"_id": {"$oid": "57985aa6aafbb30e5e2e076b"}, "item": 1}'
'{"_id": {"$oid": "57985aa6aafbb30e5e2e076b"}, "item": 11}'

which is the correct result.

Now change the model to

class TestDoc1(Document):
    items = IntField()
t_d = TestDoc1()
t_d.items = 1
t_d.save()
TestDoc1.objects(id=t_d.id).update(inc__items = 10)
t_d.to_json()
t_d.reload()
t_d.to_json()

Results in

'{"_id": {"$oid": "57985be1aafbb30e5e2e076c"}, "items": 1}'
'{"_id": {"$oid": "57985be1aafbb30e5e2e076c"}, "items": 1}'

which is not the incorrect one.

Is there something which I am doing wrong or this is by design.

TIA :)

Reproduce the issue with the two TestDoc and TestDoc1 snippets, focusing on the difference between the item and items fields. Trace the Document.reload entry point and verify that the items value changes from 1 to 11 after the database increment, without changing the working item case.