This would be used in a chosen plaintext attack, right? If you saw a ciphertext C1 with IV1, and you were able to choose the following Pj and predict the corresponding IVj, then you could verify whether the plaintext of C1 was P1~ by choosing Pj = P1~ XOR IV1 XOR IVj, so that Cj = C1 iff Pj = P1~. This would allow you to test likely values of P1~ from a dictionary.