Netherrack doesn't stop burning.
That's what I tried too. I built one outside, but the fire travelled through the stone I had place around it and caught some wool on fire.
Also, I'm using hmod on a server that I'm running for a me and a couple of friends. I'm placing leaves to use as bushes, and it was working great earlier but now for some reason every leaf block I put down "falls" and disappears. The ones I placed earlier are still sitting fine, as long as I don't place a new block anywhere near them. If I place a new one next to an old one, it makes it fall too.
edit: nvm about the leaves. I haven't figured out what was causing it but I fixed the problem by placed logs in the ground ever so often. You can't see them unless you're looking for them.