Decrypting an encrypted aes 256 cbc text with random IV, decrypts the string
Here is the picture for CBC decryption ($\oplus$ is the XOR operation of each bit/byte at the same position of the input blocks):



As you can see only the first block is altered by the IV.

During encryption every block is changed because the ciphertext will propagate the uniqueness of the IV over all subsequent blocks. However, during decryption only the first block is XOR'ed with the IV to get back the first block of plaintext.

If that block is random then the result will also be random. The rest of the blocks is unaffected.

If you change just a single bit of the original IV, then only that particular bit in the plaintext block will be affected.