How can you distinguish a cipher composed only of a Feistel network from a random function if it has only (a) one round, (b) two rounds?

For clarity, here is an image of such a cipher with two rounds:

A sequence of plaintext blocks M1, . . . , M8 is encrypted using DES into a sequence of ciphertext blocks. Where an IV is used, it is numbered C0. A transmission error occurs and one bit in ciphertext block C3 changes its value. As a consequence, the receiver obtains after decryption a corrupted plaintext block sequence M1′,…,M8′. For the discussed modes of operation (ECB, CBC), how many bits do you expect to be wrong in each block Mi′? (Hint: You may find it helpful to draw decryption block diagrams.)

Please motivate your answer.