Hello everyone,
My coworker found this and shared it with me today. I have tested to see VFP apps correctly show the MDI form with a theme in Windows Server 2012. If you have a github account and would like to vote this up. I say thank you!
https://github.com/dotnet/winforms/issues/3691
It's not just a Winforms issue, it's a Windows base code issue. I hope it gets fixed.
Have a good one! Tracy