According to Osho, Tirthankaras are not bound by compassion-born karma because their 'doing' is non-doing: there is no sense of doer, no reactive emotion triggering action. Their compassion is an overflowing state - compassion-full - not a response to others' suffering. Like breathing or a lamp's light, it simply happens. Karma binds only when intention, ego, and disturbance are present; in them, these are absent.
They don’t collect karma because no ego is acting—compassion just overflows naturally, like a lamp that shines on its own.