Does Windows not ensure that the UEFI boots back into Windows when it does an auto-reboot for updates? There's a UEFI variable called BootNext which Windows already knows how to use since the advanced startup options must be setting it to allow rebooting directly to the UEFI settings.
Given that Windows tries to restore open windows to make it look like it didn't even reboot, I'm surprised they wouldn't make sure that the reboot actually goes back into Windows.
No, it doesn't. Even a sysprepped image of Windows (which thus runs Setup to install drivers and finalize the installation) doesn't change the boot order on UEFI machines. I think just the installer does this when you first install Windows.
That's so weird. Normally I don't want my OS changing what is booted into on a whim, but going back into the same OS for cases like these just seems like sane behavior to me.
There's good reason you might not want that behavior, and no reason to enforce it. Booting an alternate OS doesn't interrupt Windows update operations.
Not in my experience. For my typical dual boot situation where Grub is installed as the bootloader, I have to update the Grub settings like so to allow Windows updates to go smoothly:
I am not certain about this, but I think that these options no longer work on UEFI machines. GRUB does not have control over what options are presented if GRUB isn't the selected bootloader. This stuff is BIOS-only.
I have this working on a UEFI system. You select your Linux drive in the UEFI configuration (so the computer always boots into GRUB) and then GRUB will boot into Linux or Windows depending on the last saved option.
The GRUB_DEFAULT and GRUB_SAVE_DEFAULT settings don't affect the UEFI settings, they only affect the default boot option in GRUB's boot menu. From the UEFI configuration perspective, the boot option never changes and it's always set as the drive with GRUB installed on it.
Given that Windows tries to restore open windows to make it look like it didn't even reboot, I'm surprised they wouldn't make sure that the reboot actually goes back into Windows.