So my account is US, my Xboxes are US NTSC, and I've never migrated across regions. I use no proxy, and my IP resolves to a specifically American host. Despite this, since the website update getting ready for Xbox One, Xbox.com suddenly says I'm from the UK. Any page I load directs me to the en-GB page unless I specifically re-enter en-US, and even then it lasts at best one page load.
Is there a setting I'm missing or is this all from your end?