DESK.CPL does not show correct theme preview in Windows 7

I tried to run the DESK.CPL applet of ReactOS in Windows 7 and I discovered that the preview of the themes is corrupted, see attached screenshot.
According to:

https://msdn.microsoft.com/en-us/library/windows/desktop/ff729175%28v=vs.85%29.aspx

NONCLIENTMETRICS has different size if WINVER >= 0x0600, I did an experiment by forcing a greater version, but it did not solve the problem, so it should be something else.
Instead, the classic theme is drawn correctly, because the built-in control in the CPL does all the work without using uxtheme.