Understanding aiohttp.TCPConnector pooling & connection limits

I am experimenting with the limit and limit_per_host parameters to aiohttp.connector.TCPConnector.

In the script below, I pass connector = aiohttp.connector.TCPConnector(limit=25, limit_per_host=5) to aiohttp.ClientSession, then open 2 requests to docs.aiohttp.org and 3 to github.com.

The result of session.request is an instance of aiohttp.ClientResponse, and in this example I intentionally do not call .close() on it, either via .close() or __aexit__. I would assume this would leave the connection pool open and decrease the available connections to that (host, ssl, port) triple by -1.

The table below represents the ._available_connections() after each request. Why does the number hang at 4 even after completing the 2nd request to docs.aiohttp.org? Both of these connections are presumably still open and haven't accessed ._content yet or been closed. Shouldn't the available connections decrease by 1?

After Request Num.        To                    _available_connections
1                         docs.aiohttp.org      4
2                         docs.aiohttp.org      4   <--- Why?
3                         github.com            4
4                         github.com            3
5                         github.com            2

Furthermore, why does ._acquired_per_host only ever contain 1 key? I guess I may be understanding the methods of TCPConnector; what explains the behavior above?

Full script:

import aiohttp


async def main():
    connector = aiohttp.connector.TCPConnector(limit=25, limit_per_host=5)

    print("Connector arguments:")
    print("_limit:", connector._limit)
    print("_limit_per_host:", connector._limit_per_host)
    print("-" * 70, end="\n\n")

    async with aiohttp.client.ClientSession(
        connector=connector,
        headers={"User-Agent": "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2225.0 Safari/537.36"},
        raise_for_status=True
    ) as session:

        # Make 2 connections to docs.aiohttp.org and 
        #      3 connections to github.com
        #
        # Note that these instances intentionally do not use
        # .close(), either explicitly or via __aexit__
        # in an async with block

        r1 = await session.request(
            "GET",
            "https://docs.aiohttp.org/en/stable/client_reference.html#connectors"
        )
        print_connector_attrs("r1", session)

        r2 = await session.request(
            "GET",
            "https://docs.aiohttp.org/en/stable/index.html"
        )
        print_connector_attrs("r2", session)

        r3 = await session.request(
            "GET",
            "https://github.com/aio-libs/aiohttp/blob/master/aiohttp/client.py"
        )
        print_connector_attrs("r3", session)

        r4 = await session.request(
            "GET",
            "https://github.com/python/cpython/blob/3.7/Lib/typing.py"
        )
        print_connector_attrs("r4", session)

        r5 = await session.request(
            "GET",
            "https://github.com/aio-libs/aiohttp"
        )
        print_connector_attrs("r5", session)


def print_connector_attrs(name: str, session: aiohttp.client.ClientSession):
    print("Connection attributes for", name, end="\n\n")
    conn = session._connector
    print("_conns:", conn._conns, end="\n\n")
    print("_acquired:", conn._acquired, end="\n\n")
    print("_acquired_per_host:", conn._acquired_per_host, end="\n\n")
    print("_available_connections:")
    for k in conn._acquired_per_host:
        print("\t", k, conn._available_connections(k))
    print("-" * 70, end="\n\n")


if __name__ == "__main__":
    import asyncio
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

The output is pasted at https://pastebin.com/rvfzMTe3. I've put it there rather than here because the lines are long and not very wrap-able.

from Understanding aiohttp.TCPConnector pooling & connection limits