Hello Brad,
I tested the described scenario, but I couldn't reproduce the issue that you described.
On a Windows 7 with "Windows 7 Basic" theme with the version of the assemblies 11.12.14.12
I created a new NForm and in the constructor I set a custom frame as follows:
NFrameAppearance appearance = NUIManager.GetPredefinedFrame(PredefinedFrame.Simple);
FrameAppearance = appearance;
Is there anything else in your code regarding the form which I can set in order to reproduce the problem?
Best Regards,
Nevron Support Team