According to my experience the Dropbox folder is treated by users as a shared [network] folder.
So the expected default behaviour of the drag-and-drop between the Dropbox folder and local folders is the copy [instead of move] operation.
The move operation leads to the loss of the original files in shared folder when user means to copy it to a local folder from a shared [network] folder. That causes a bad user experience with Dropbox.
The Dropbox should have an option to set the default action of drag-and-drop between the Dropbox folder and local folders. The default should be copy.
BTW the Google Stream (Google Drive) drag-and-drop between the Google folder and local folders the default operation is the copy and that is the way as it should be.
