Question about rf-string and r-string

I notice that I have used rf-strings in a few solutions, for example here: https://py.checkio.org/mission/double-substring/publications/Guest_5a80b5eb/python-3/first/

However, I notice that my "features used" progress tracker does not include rf-string or r-string. It does include f-string.

Does anyone know how exactly you get credit for rf-string? This seems to be a CheckiO bug.

I have tried submitting solutions with all of the following format:

newline = '\n'
print(
    rf'1\100{newline}'
    rf"1\100{newline}"
    RF'1\100{newline}'
    RF"1\100{newline}"
    fr'1\100{newline}'
    fr"1\100{newline}"
    FR'1\100{newline}'
    FR"1\100{newline}")

All of these forms work, but none of them register rf-string as used.