Really sorry if this has been answered elsewhere or before, but I have searched everywhere I can think of using every combination of keywords and can't seem to find a solution to my problem.
I did find someone asking the same question on Magento's forums, but it was never solved (http://www.magentocommerce.com/boards%20/viewthread/308501/)
Anyway I'm creating a store in Magento CE 1.8.1, which basically I want to only allow people to use the United Kingdom for their billing and shipping addresses. When I set System > Configuration > General > Countries Options > Allow Countries: to just the United Kingdom this works perfectly - i.e. on all checkout combinations whether guest, register or existing member, the only option under country for any address is United Kingdom.
However I then place a few test orders through the front end of the site, and then suddenly, seemingly at random during one of the orders the country drop-down will be back to default and from then on all address input forms will show all countries for selection.
Does anybody know why this might be or what steps I can take to track down why this is happening? When I go back into the admin the Allow Countries option seems to still be just on United Kingdom. However if I unselect it, reselect it, flush the cache and reindex then the behaviour of the country drop-down is back exactly as I want it again (i.e. just the United Kingdom).
I'm using the 1 page checkout and Ultimo theme. I've modified some aspects of the fontend templates, but nothing major, and have not modified anything in the backend/core. I have 5 extensions installed if that makes any difference: Magento Color Picker for Products by Orange35, Mass Product Relater by Iksanika, Contacts Form Captcha by Oleg_Koval, Fooman Same Order Invoice Number and Orders Eraser by Wyomind.
Thanks in advance for any help anyone can offer.