High availability primary does not automatically take secondary role when back online

Setup: * Basic high availability * 2 replicas (1 primary, 1 secondary). DB01 => initial primary. DB02 => initial secondary * Synchronous commit on both * Both are in synchronized state * There is no listener configured * Cluster type None When we stop the DB01 (initial & current primary) SQL service using services.msc (simulating a friendly server crash) and then initiate a forced failover on DB02 (initial & current secondary) using: ALTER AVAILABILITY GROUP [TestHA] FORCE_FAILOVER_ALLOW_DATA_LOSS; The secondary database comes online, which is what we want. However, when the DB01 SQL Server service is started again, using services.msc, the DB01 db assumes *primary* role again. So currently there are 2 instances readable/writable and out of sync. We were expecting that the initial primary would detect that a secondary has taken the primary role and assume a secondary role or at least be inaccessible so apps cannot work on old data. The same procedure, but using the deprecated mirror setup, does behave this way.