[enhancement] witch water should convert lava source to black stone, instead of obsidian

[FCWYzzr]

When lava flows above a water barrel, water will be convert to stone, the same block when lava touches water (from above)
When water flows above a lava barrel, lava will be convert to obsidian, the same block when water touches lava (source)
When lava flows above a witch water barrel, witch water will be convert to netherack, the same block when lava touches witch water.
Yet when witch water touches lava source, lava source will be converted to obsidian instead of black stone, the block product by lava barrel when witch water flows over then