I’ll be honest: I don’t know squat about HDV. However can surmise:
i imagine it’s like DVCPRO-HD. In order to keep data rate down, HDV films in 1440×1080 anamorphic: it’s MEANT to be stretched sideways to fill 1920×1080. So when you see it in FCP with black bars on the sides, something has been set wrong. You’re seeing yourself skinner (sorry! tough breaks!)
Again, I’m just guessing. A good way to confirm if your aspect ratio is correct is to create a circle and rotate it: if it wobbles then something is off.