DES 1-bit changes to inputs: why when I change two inputs by only one bit I get predictable results?
DES block size is 64 bits, your input is 3 DES blocks, you change 1 bit in the first input block only and encrypt the whole input in ECB mode without padding; the first output block is completely different after the change, the 2nd and 3rd blocks are the same, as it should be.

Here's the ECB mode of operation: