Upload & Sell: Off
You're right. If that is the issue, they should have.
It wouldn't matter. If mismarking is the issue, they are prohibited by federal law from putting it on an aircraft, x-rayed or not. Putting it on hold and calling you is the best they can do.
Brian is right If your going to ship something by air, especially over seas, you need to use an unmarked box. I have been shipping things all over the place and this has been a policy by most shippers for years now. FeEx always inspects any package I ship that is insured over $500. They open it up, examine the contents and packaging, and retape it. On some ocassions I have used brown tape to cover writing but only on ground shipments.
You have to be a smart shipper these days to avoid problems and delays.