i have to agree with chef's slaad. my own heavy-handed DM methods cost me a great player. i was thwarting class abilities simply because i felt they were ruinging my plot. player got fed up and left, rightly claiming that i was not willing to let the class abilities work the way they should.
i have since learned that it's best if you prepare for the class abilities, and then alter npc reactions accordingly. for instance, let rhivadi SEE the warlock see her. assuming she knows him by that point, she can make his life a virtual hell in order to keep her secret.
at low levels he ain't gonna understand half of what he's seeing anyway - and any 10th level wizard could make see invisibil permanent on himself anyway. i don't think it's a game-breaker, instead i have learned to see it as a wonderful dmming and role-playing opportunity.