On each occasion I corrected the entry on the drop down menu from United States to United Kingdom - it stayed as United Kingdom while I was on the page but when the page was loaded once more on a subsequent attempt at payment (a few minutes on each occasion) it read United States even though all the other details of my address had been retained correctly.

My first attempt at a purchase was actually something like friday evening where I was unable to proceed due to this problem - I remember the United States being listed as my home country then and corrected it. The subsequent four attempts were all in the space of about ten minutes yesterday evening UK time... so mid to late afternoon your time on Sunday (depending where you are in the US).

Hope this helps