ftinspect doesn't select named instances and/or subfonts in VF TTCs

If I call ftinspect on this Noto CJK VF font, the up and down arrows at the bottom of the main window to select subfonts in a TTC and named instances, respectively, do nothing.

Non-VF TTCs seem to work fine. Selection of named instances in Non-TTC VFs like this one, however, doesn't work either.