1) Files get duplicated (copied) when dragged between desktop and Thunar window;

And when you hold the Ctrl of Shift button (I'm not using desktop icons so I don't really know)?

Xfdesktop doesn't support all the Thunar features, because the code cannot be shared easily (thumbnailer code for example). Xfdesktop also uses a custom icon view grid, so selecting multiple files (ak. rubberbanding) is not possible. This will be fixed in the feature because Thunar will also manage the desktop (replace xfdesktop for filesystem icons).

From what I have read about xfdesktop, it utilizes Thunar's libraries, integrates with Thunar, etc. But I am having two issues, that I cannot manage to resolve:

1) Files get duplicated (copied) when dragged between desktop and Thunar window;
2) There's no thumbnailer, and I cannot select several files by mouse-dragging: desktop does not behave like Thunar at all...

Are these xfdesktop limitations, or am I doing something plain wrong?