I've installed Windows 10 with Guest Additions running on macOS Sierra and it works fine on the full screen.
However it generated after some time extra blank screen, then after another one as shown below:
1. macOS Desktop, 2. Blank screen. 3. The only working guest system's desktop. 4. Another blank screen.
On these blank screens nothing works (no left/right clicks), apart of the VirtualBox VM menu where I can only quit the VM, which will shutdown the main VM (no any other menus on the edges).
Secondly guest system (Windows) isn't aware of these extra displays since it detects only 1 and it didn't detect another display, see:
Why this is happening, and how to get rid or prevent creation of these blank screens?
VirtualBox: 5.1.10
