Perhaps your machine crashes occasionally.
On reboot the installations take place.
Run Windows update manually when you know there is a worthy patch.
Then you know exactly what is happening and when.
If your machine still reboots you know there is a problem that needs locking down.
Machine doesn't crash, and I get the popup notification that updates have been installed when I login in the morning.
Only way to avoid this is to completely turn updates off. Then I have to wait for windows to look for updates, click install, wait for them to download and install, and then clicking ok to reboot.
Why does the setting "Download updates but let me choose when to install them" on Windows 7 function differently than it does on Server 2008/2012 ? And why does it automatically install updates and reboot when it sees a critical update?