When I left-click and drag to the desktop, when the cursor dragging the object finally gets outside of the host folder and over the desktop, I get a flyout that says "+ copy to desktop". When I release the mouse button the file has actually been duplicated (i.e. copied) onto the desktop, and the copy actually lives in the desktop folder.
But then my source folder is on a different drive (H) than my desktop folder (C), so the default action is "copy".
In order to get a MOVE from H to C, I have to right-click drag. It still shows the same "+ copy to desktop" when the cursor reaches the desktop area, but when I release the mouse button the expected menu now pops up asking me to select move here, copy here, create shortcuts here, or cancel.
This is all as expected. No big revelation.
When I repeat the same left-click drag from a file on a folder on the C drive itself, when the cursor reaches the desktop area the popup shows "-> move to desktop", and when I release the mouse button the file actually does move to the desktop, getting deleted from the source folder.
Same with right-click drag, and on the popup after releasing the mouse button the "move to desktop" item is in bold, indicating it as the default action.
What happens in your case? What external symptoms result from your cursor-drag and then release?