Do not know if this is repost, do hope it isn't, and rumor has it this was fixed but hasn't (Due to the lose of a 100 points for the same exploit).
In Dalaran Sewers, a lock can drop a portal atop of the sewer gate and jump down. Once your pet is dead, they do not have to waste a quick summon, they can simply teleport back up and slow summon. Sucky blizzard cannot keep up to their word.... /sigh