I was going to post this on the official server...

[Scaerick]

... some kind of strange lag involving my Drain Soul spell (I just keep draining long after the target is dead)

That's just a Warlock bug... sometimes when you're channelling Drain Life or Drain Soul and the target dies, the 'gimme' energy beam just hangs out for a while after... most often when the cast coincides almost exactly with the death (happens all the time for me in those 'crap i could use a soul shard' moments right when the mob's at a sliver).