Worldborder does not take nether coordinates into account

What happens:

1. Set the world border to a lower value.
2. Go into the nether and place a nether portal at a location which would place you at overworld coordinates behind the world border.
3. See how you will instantly die (in survival).

What should happen:

The player should not be allowed to enter a nether portal which kills him due to the world border in the overworld or the world border should reflect the coordinate ratio between overworld and nether.