Collectible Card Game Headquarters

Describe the Bug:
The most common card to attach is Eldrazi Conscription, but it seems to get attached just after the attack phase starts so that you miss out on the "annihilator" effect.

Which card did behave improperly ?
Sovereigns of Lost Alara

Which update are you using?(date,name)Which type(Duel,Gauntlet,Sealed Deck)
25 March 2015: Fate Reforged / Gauntlet (but not challenge)

What exactly should be the correct behavior/interaction ?
It should attach the enchantment card and then the attack phase should start.

Are any other cards possibly affected by this bug ?
Not sure

Sovereigns and annihilator both trigger for an attack declaration. By the time Sovereigns' trigger resolves, it's too late for anything it fetches to trigger. Working as designed.