Hi Graham,
Thank you for your inquiry, we have done some testing regarding this, we can see some of the SKU's have this problem while the others don't.
Can you let us know what's the name of the SKU in question? It might be helpful for us to investigate the problem. Thanks in advance.
We're currently investigating this problem. As soon as we have a result, we will let you know. Thank you for your patience with us on this.
--Peng