BIG-IP 11.6 Auto Failback disabled, but devices auto failbacks

Hi,

we have two Viprion 2400 chassis, each with one blade running BIG-IP 11.6 HF4.

There is sync-failover device group with default traffic-group with disabled auto failback.

Problem is that after we reboot current active device, second device become active (which is OK), but after rebooted device boots up it takes active role.

We do not want this auto failback (preempt) behaviour. How can we accomplish this?