It’s not a bug, its an undocumented feature

Windows 10 Fall Creators Update has a new "feature" which re-opens all running applications upon next boot if you do not close programs before you shutdown.

As a workaround to this "bug-feature", create a shortcut as follows on your task-bar or desktop.

To Shutdown:

shutdown.exe /s /t 0

To Reboot:

shutdown.exe /r /t 0

Unfortunately, at the time of this writing, there is no way to switch this feature off within windows settings. Hopefully, Microsoft includes a switch in coming updates!