I have installs of Win7 on WSP12 and they go fullscreen without issue.
I upgraded one of the Win7 installs to Win10, and when it completed, the desktop does not expand to the full screen size when I click the fullscreen icon on the WSP menubar at the top. I've tried playing around with resolution settings in Win10 and manually setting resolutions in WSP for that VM, but no joy so far.
How do I get fullscreen mode (with the whole desktop filling the screen) with Win10 under WSP12?