Thumbnails have black background
Question / Problem
Why do the thumbnails have an ugly black background?
Answer / Solution
The thumbnail images show a black background if your application does not include a proper XP manifest. Windows then loads the old Windows 2000 version of ComCtl32.DLL which cannot deal properly with alpha channels.
To solve this please include the unit "XpMan" somewhere in your project or set "Project > Options > Application > Runtime Themes" to the value "Enable runtime themes".