Well, it looks like the Warlocks have been getting the short end of the stick for some time. Now Blizzard hasn't nerfed them, but their pet Imp instead.

According to Drysc, the Imps were performing far better than they expected. They'll be implementing a hotfix tonight that will temporarily remove the Imp's spell damage coefficient and "remove any spell damage bonuses from improving the Imp’s attacks." Here's what he had to say:

We are currently on schedule to be implementing the correct values with the next patch. While we are able to effectively block the spell damage bonus with a hotfix it will require a client side patch to input the intended spell damage bonus the Imp is receiving.