I just realised that I have totally missed this and didn't know it was happening from 2010. I've had about 100 sales to US since then and probably about 1/3 of them have had that security charge. So about $300 lost on this just out of my own carelessness.

I am still amazed though and completely do not understand why the ebay postage calculator is not being fixed. I have a simple postage calculator in my on-line store, it links directly to Australia post - the charges for US customers are returned correctly, they include the $9 security charge. Why is this not being addressed? Is there a way of communicating with ebay with regards to this? I have raised a technical ticket with them but not sure that this is the best way to go. It is just baffling - aren't they realising that they are losing a lot of money by not fixing this problem?