Here's an example of the behaviour:

import io

def test(buf):
   textio = io.TextIOWrapper(buf)

buf = io.BytesIO()
test(buf)
print(buf.closed)  # This prints True currently


The problem here is TextIOWrapper closes its buffer when deleted.
BufferedRWPair behalves similarly. The solution is simply to override
the __del__ method of TextIOWrapper inherited from IOBase.

You can call the detach() method if you don't want to the underlying
stream to be closed.
We could also add a close_parent attribute defaulting to True.

OK I am convinced, the current behavior is fine. Let's close this one.