Or, maybe you should stop being such a metagamer and accept that the title 'warlock' might actualy be given to a priest!
Theres no rule that A wizard can't also be a mercenary, or that a barbarian can't be a knight. The only rule I can think of is that a Paladin cannot be a rogue, but I've seen cases where even that can stand. The only place those limitations exist is from being used at thinking outside the RP box, such as 'X said bash the door down, so that must mean I need to have a skill called bash on my character sheet' etc.
Oh well, such will happen in a roleplaying game where the GM is not always watching over the players.
Just my two copper on the matter