(1) A proxy becomes revocable, notwithstanding a provision making it irrevocable, after the pledge is redeemed or the security interest is terminated, or the debt of the corporation is paid, or the period of employment provided for in the contract of employment has terminated, or the agreement under section 461 has terminated. In a case provided for in section 422(c) or (d), the proxy is revocable 3 years after the date of the proxy or at the end of any period specified in the proxy, whichever period is less, unless the period of irrevocability is renewed by execution of a new irrevocable proxy. This subsection does not affect the duration of a proxy under section 421(2).

    (2) A proxy is revocable, notwithstanding a provision making it irrevocable, by a purchaser of shares who did not know of the existence of the provision unless the existence of the proxy and its irrevocability are noted conspicuously on the face or back of the certificate representing the shares.