#10 - April 23, 2015, 8:26 p.m.
Yeah, this trick has been in the game since Grimoire of Sacrifice was introduced. The version of Spell Lock that Felhunters use is technically a different ability than the version granted to the Warlock through Grimoire of Sacrifice, due to the way Sacrifice works behind the scenes, and they don't have a shared cooldown.
I don't think we're particularly worried about this trick in terms of overall balance, but I can bring it up with the dev team again.