I've been testing my bootable backup with my MBP 2018, and I've noticed a peculiar behavior that wasn't present on my 2012 MBP. When I first restart after changing startup disk, the machine will restart itself once early on in the boot process. If changing startup disk via System Preferences, this will occur shortly after the Apple logo appears. If changing disk via Startup Manager menu (holding option on boot), this will occur immediately after selecting the new disk. The machine then proceeds to boot from the desired disk. The restart does not occur if I continue to restart using the same disk. It only occurs on first restart after selecting a new disk. This happens even when switching back to the internal drive. Startup security settings have Secure Boot set to "full security" and External Boot set to Allow. Has anyone else noticed this behavior?