Any acquisition or disposition of an equity security or certificate representing equity securities involved in the deposit or withdrawal from a voting trust or deposit agreement shall be exempt from Section 16(b) of the Act if substantially all of the assets held under the voting trust or deposit agreement immediately after the deposit or immediately prior to the withdrawal consisted of equity securities of the same class as the security deposited or withdrawn: Provided, however, That this exemption shall not apply if there is a non-exempt purchase or sale of an equity security of the class deposited within six months (including the date of withdrawal or deposit) of a non-exempt sale or purchase, respectively, of any certificate representing such equity security (other than the actual deposit or withdrawal).