Originally Posted by Andrew R Stewart

This happened because you used your bike, and likely didn't replace cables as frequently as you obviously should have. We see this casing strands migrating lengthwise often enough. On cheap as well as quality bikes. But, regardless of my somewhat tongue in cheek opening, I have never yet had anyone explain why it happens to the green bike but not the blue one given both having a similar situation. We have concluded that the short term fix is simple, replace the casing loops (and inner cable as precaution). The long term avoidance is monitoring and servicing more frequently.