Incorrect usage of `Converter.TryConvertToString`?

It looks like Converter.TryConvertToString converts user defined types to strings if they define __str__. I have no idea is this is the correct behaviour for this method? This causes some things to "work" when they probably shouldn't. For example:

class notstr:
    def __str__(self):
        return "test"

try:
    "".join([notstr()])
    assert False
except TypeError:
    pass

try:
    class test:
        __slots__ = [notstr()]
    assert False
except TypeError as e:
    pass

Begin at Converter.TryConvertToString and reproduce the two Python examples from the issue. The intended behavior is not specified, so confirm whether user-defined str conversions should be accepted before changing anything; done means the method and both examples consistently follow the decided semantics.