The Bug:

Lava lake generate in icebergs.

Steps to Reproduce:

1. Create a world with the seed 102
2. You will see stone generated in the iceberg, run /tp 258 70 226
3. Break the closest nearby exposed stone blocks that are on the iceberg to observe the lava, or go into spectator mode and look inside.

Observed Results:

 Lava lakes are able to generate in an iceberg.

Expected Results:

No lava lakes should be generating in icebergs.

The Fix:

This issue is fixable by adding packed ice to the minecraft:lava_pool_stone_cannot_replace tag.