I have seen several reports on the US discussion boards of users in the UK and Australia saying that they are being redirected to the US site when selecting categories to search on the main ebay.co.uk or ebay.com.au page or search results page without using any keywords using the category drop-down on the right side of the search entry field. Try avoiding searching that way; you can add keywords and search, or else choose the categories using the "Shop by category" links on the left side of the search entry field.
If possible, try erasing your ebay.com browser cookies -- that way if you are redirected again, you will be forced to sign in, making more likely you will notice.
