Starlette: accumulated tasks. Why?

[lifemaker]

Hi everyone!
I have test project:

    from starlette.applications import Starlette
    from starlette.responses import JSONResponse
    from starlette.routing import Route
    
    from starlette.requests import Request
    from starlette.background import BackgroundTasks, BackgroundTask
    
    
    def parse_json(json_data):
        print(json_data['value'])
    
    
    async def testbground(request: Request):
        try:
            json_data = await request.json()
        except JSONDecodeError:
            print('cannot_parse_request_body')
            raise HTTPException(status_code=HTTP_400_BAD_REQUEST, detail='cannot_parse_request_body')
        except:
            return JSONResponse({"status": "Error"}, status_code=500)
    
        if 'value' in json_data.keys():
            tasks.add_task(parse_json, json_data)
        else:
            raise HTTPException(status_code=HTTP_400_BAD_REQUEST, detail='wrong_json_format')
    
        return JSONResponse({"status": "OK"}, background=tasks, status_code=200)
    
    
    
    
    tasks = BackgroundTasks()
    
    app = Starlette(debug=True, routes=[
        Route('/testbground', endpoint=testbground, methods=['POST']),
    ])

And have sender.py for tests:

    import requests
    
    url = 'http://localhost:8000/testbground'
    
    for i in range(10):
        data = {'value': i}
    
        try:
            r = requests.post(url, json=data, timeout=5)
        except Exception as e:
            print(e)

Result:

Output:
    0
    0 1
    0 1 2
    0 1 2 3
    ...
    0 1 2 3 4 5 6 7 8 9

But I was expecting another result.

Output:
    0 
    1 
    2 
    ... 
    9

What is wrong? How can i add tasks to pull right?