Clockwork Alpha
Skeletron Prime
So, I was building a hellevator... Then finally when I got to hell. Like 7 blocks deep of lava spawned over me, almost killing me. Is this some sort of glitch?
I would take a guess and say that you mined straight(-ish) down through lava, and due to the current liquid mechanics of Terraria, the lava lagged so much that it had to force-settle all at one time, making it look like a bunch of lava "spawned" over you.
This may be it. I use sand and silt to tunnel by lava while using buckets to clear out lava directly below me. I remember lava and water sometimes getting through, but I'm not sure how the silt lets water or lava through.