I found this info on the web :
I have disassembled a Shuffle 4G cable. Under its Type-A USB
connector's cover is a small pcb carrying three chips and a
few passive components. One of them is a leggy chip that
could well be a microcontroller.
So this cable is active for sure and this would explain the
high-impedance state of the powered-down cable. It would be
helpful if another user could pry-open the cover of their
3G/4G cable, I believe these are the same, and check this
embedded chip existence.
Worryingly, such a design creates a horrible opportunity to
create malicious USB exploit cables and passed-off as
innocuous Apple originals. I note that there are plenty of
Shuffle 4G USB cables on eBay. I say worryingly because my
cable ''is'' a replacement from eBay - I'd lost the original
cable.
Another curious and perhaps revealing situation I found. I
tried connecting an Archos cable which is wired pin-to-pin
in the same manner as the 1G/2G shuffles - It worked; yet
only once. This one-off behaviour was repeated on a second
machine, where it worked, but just the once. thereafter the
Shuffle was completely invisible to the computers using this
cable.