Hi there.
Last time I was on the PTR (5 or less days ago) I was playing on my 39 Warlock, killing some mobs. Then I was thinking of the old Divine Favor bug, where you could get two criticals in a row (holy light + spam holy shock), so I came to think; let's try that with Soulburn - Spell - World of Warcraft .
As you can see, it gives a couple bonuses to your spells.
The thing I've tried (not having soul fire yet etc..) was this;
1. Cast Soulburn
2. Cast Searing Pain
3. Spam Drain Life / Pet summon
You will then see you'll get a 100% crit chance on Searing Pain, and still get the bonus for drain life / instant pet summon.
I'm guessing this will work the same way with soul fire, soulburn > searing pain > spam soul fire.
I haven't reported this bug, and haven't seen any thread on the PTR forums about it, so when somebody can confirm it went to live, please post it here.