Vegetation (dead bush, grass and flowers) can generate on the magma and netherrack from ruined portals

I was flying around in this new beta version and noticed that the some of the flowers were spawning on blocks they cant be placed on then just breaking so they are left floating.

Seed: 123
Coords: -9248 63 874
Coords: -8629 112 -330

Steps to reproduce:

1. Create a world with the specified seed.
2. Visit the specified coordinates.

Observed results:
Notice that flowers and grass have generated on the ruined portal.

Expected results:
Flowers and grass should not be generated on the ruined portal.