In reply to Wingnut: Found out that in this case it was my "fault", my PC at work gets awkward with properly ejecting a certain USB stick so I tend to get impatient and just pull it out. Usually I get away with it (or perhaps the corrupted files go undetected; but in this case as there were just 3 files on the stick, the last one got corrupted?)
It actually shows up just fine on this PC but I got a colleague to check it and it was just gobbledygook on his laptop.
So might that be the case with you?
(everything else I said above, is definitely a Jessops problem)