Not sure if anyone else has noticed this on the PTR but Soul Leech now stacks to 30% of the lock's max HP. On live, Soul Leech stacks to 100% of the locks HP. So if you go by the PTR patch notes, it looks like SL received a small buffed by adding in Shadowburn for destro but the sad truth is that they nerfed it and didn't post a note for it. If you have a weakaura for this just pay attention to the strength of the bubble when you get on the PTR or you can mouseover the buff while hitting a raid dummy.