The liquids are introduced by extending water when they should extending lava or at least use a correct temperature (1300) or tag. A possible tag would be minecraft:lava. The reason this is a problem, is in its interactions with other mods, which use liquid temperatures such as tinkers or wood/ceramic buckets.

Bump again, but I realize this could be halfway done in Forge. No word for Fabric.

Have not touched upon this for a while as fluid properties, especially cross-platform, are scant