I ran into the same problem just now, that the policy reset itself using 2 servers with names “p1” and “p2”. I could not save the inverted order of first field “p2” and then “p1”. Fortunately I have one server with a different name.
So I updated the policy to “p2”, “different_name” and saved. Then edited again to “p2”, “p1” and saved and that worked. Hope it helps someone.
Possibly a bug in the policy system.
Plus I think that the article Changing the primary LDAP Server to redistribute the Server load should at least mention the option of using a policy.