They dont know that was Planar Binded, Sorry. Subtle spells are imperceptible.
Really? 30 INT doesnt know what is a Wizard. Hahah
Yes, but the spellcaster ACTUALLY GIVING THE ORDER, which isn't part of the spell, is EMINENTLY perceptible. How can you imagine anyone obeying orders if he can't perceive the order given... That's when Sul Khathesh killed the Moronic One, when he gave orders AFTER SHE SUCCESSFULLY resisted the spell. Given enough try, she'll fail the saving throw, but she won't let Moronic Out get out saying "sorry to have bothered you with my order, see you soon!".