Thanks - I've never heard of this happening. Maybe the adjusting bolt turned in a way that unwound the strands? I suspect this weakens the cable a small amount along that length, but I don't think it would be excessive. It WOULD cause the cable to lengthen somewhat there.
Edit: It's possible the stress on the individual strands are no longer equal in the area where it's unwound. This might cause those strands to start breaking, which would in turn increase the stress on the remaining strands, leading to a "cascading" effect. I'd keep an eye on that portion for a while and replace the cable if you notice any fraying.
- Jack