This is working as intended like many said.
they changed it in a patch so that it is resummoned.
not an exploit.
As stated by our guild's top-dpsing warlock.
"Shadow is superior to fire in every way imaginable, unless your idea of PvE raiding is killing mobs in Terokkar or you don"t have shards to sacrifice succi with in actual raid. So if you didn"t get my point here it goes again: SHADOW IS BETTER SHADOW IS BETTER SHADOW IS BETTER SHADOW IS BETTER SHADOW IS BETTER SHADOW IS BETTER!"
Shadow is better if people are using the debuff. If you have 3-4 locks shadow is going to best raid dps. Where as fire with 1-2 mages keeping scorch up is going to be more mana efficient, and techinically neck and neck if not beating shadow.
This is coming from a warlock in a swp-1-night-clear guild.
Sorry to get off topic.