She's also not wearing a shirt
Is she weaing a swimming costume under her jacket? Maybe she went swimming in a previous scene that was then cut.
I doubt this could possibly be accidental. They have people that check keyframes. I mean, I assume she doesn't move, it's not like it's an inbetween or anything.
And then another person colours it. Obviously they noticed as they coloured her chest with skin. If they noticed and thought it a bit odd, they would tell somebody. Not just colour it and hand it to the editor.