vintagepilot, the OP has the same problem as you and will therefore get the same results. With seat 1K I assume you are taking a First class seat? They are only available for a gold, and thus they will let you, as a gold, see all that are available to a gold and will let you sit yourself in any one of them. But because you have a non-gold on the same booking reservation they will throw the error and prevent you completing the non-gold seating in a "reserved for gold" seat. Unfortunately there has never been a simple error message explaining this flaw displayed to users and lots of people have wasted many hours trying all sorts of work-arounds (without success!). Me included when I first tried this on the 1A/1K seating for me as gold and OH as a Blue.

When you are logged out it naturally shows that 1K is not available to you as you are not showing your status to the seating machine as a gold, which confirms that it is working as planned.