Wardens won't pathfind through lava even though they're immune to it. This is inconsistent with other mobs that are immune to lava, which will attempt to walk through it to get to the player if there is no other option. Java report about exactly the same problem
Steps to reproduce:
- Summon a Warden.
- Create a lava obstacle for him.
- Force the Warden to go through the lava.
Warden cannot walk on lava (despite being immune to lava).
Warden must walk and pathfind through lava.