Hi, I don't know if it should work this way and according to what I've read, no.
What happens is that when there is lava under blocks such as stone and obsidian, (which should cover fires) the blocks above are burned, it happened to me with bookstores, mysteriously disappeared because of that. I hope they fix it or say if it's normal.
I did tests
I don't think it's logical to burn things through blocks.
hmm... i thing this behavoir is normal... .
Basicly you are right that you can cover lava blocks, but the "heat" of lava and fire goes further than one block.
I never heard anything from blocks with heat protecting ability.