Sometimes you can be a bit unfortunate and hit somewhere where the hits don't get registered correctly. I feel it's usually the upper arm and shoulder area as well as the very top of the head especially. But I think we all exerience lying in a crater while a tanks mg is firing on your head and makes you see the blood come out of it while you take no damage.
However, using SMG's you usually have to be kinda unlucky when it really makes problems. It happens quite frequently, but only matters in a very few cases as other hits are lethal and it is and always was part of BF2 and its mods. Everyone is lucky and unlucky with this here and there, so I really don't mind too much and just consider those as nonlethal hits.
I'd just like the head to be bugfree though, as I expereince hitbox problems there quite often and it feels wrong. But as it can't be really fixed, let's deal with it, it's nothing more than a little annoying for a few seconds per session and therfore not a big deal to me.