I've been generating lava for a bank of magmatic engines, which are powering the crucible and the rest of my machines. I'm feeding with netherrack it via a hopper - making a trip to the nether every so often to refill.
It's worked fine for literally hours upon hours, but suddenly stopped consuming the netherrack and stopped producing lava. The magmatic engines still have a reserve in their tanks, and the crucible's power bar is full. When I take out the netherrack and swap it for cobblestone, it burns fine (it even has a higher energy requirement to burn cobble). I didn't make any changes to the power plant before it stopped working.
So what am I missing? Is this a bug? I've restarted the server and everything.