Check solution bug?

Hi, my solution is:

from typing import Tuple
def sum_by_types(items: list) -> Tuple[str, int]:
    return ''.join([_ for _ in items if isinstance(_, (str))]), sum([_ for _ in items if isinstance(_, (int))])

it passes all asserts including <sum_by_types([]) == ("", 0)>, but solution check result is:

Your result:{"checkiotype_":"tuple","values":["",0]} Right result:["",0] Fail:sumbytypes([])

I tried other solutions with same result. Bug? Or my mistake? Using Chrome.