Seems odd ebay holds you responsible though you can show you shipped. I have made the opposite experience as a recipient. The seller could show he had shipped but it never arrived. Ebay/Paypal decided it was my problem.
(Eventually I did get refunded because he had shipped uninsured and I was able to show that we agreed on insured.)
(Eventually I did get refunded because he had shipped uninsured and I was able to show that we agreed on insured.)