New lava ABM makes lava-mining weird

[o11c]

With the default ABM, mining through lava is simple: bring an infinite supply of water to the surface, and dig in. If the lava flows first, simply remove the new stone; if the water flows first (or the source moves, if water is dynamic)

With the new ABM, somehow I get obsidian on the inside of the tunnel, where the water was. This means that all higher lava will have to get turned into obsidian and mined before any progress can be made, defeating the whole point of tunneling through lava.

Overall, while the idea of "it takes sources of both kinds to create obsidian" is sound, I'm not sure all the flowing interactions accomplish anything other than spam steam particles.

In particular, what if:

• a source is allowed to move to any flowing node, rather than just its own, and
• all flowing nodes are unchanged by contact with other liquids?