Well first, there is but 1 priest, who is the elder. Second it matters little, there are another 5-6 elders, so it still won't have the 50% required.
Can you promote a new non-priest Elder? Were there more than 50% priest Elders at some point in the past? I think the game does not auto-demote people when elder priests pause or switch class, but it will forbid other non-priests to become Elders until balance is restored.
