When setting the block under soul fire to netherrack using commands, it will disappear rather than changing to the other fire type like what happens if you do it the other way round.

Steps to reproduce:

1. Place soul fire on soul soil or soul sand
2. Use the setblock command to change the block underneath to netherrack
3. The soul fire should dissappear. 

Observed results:
The soul fire disappeared

Expected results:
The soul fire turns into normal fire