Created attachment 6225 screenshoot dragging a file from one window to another leaves the icon of the file in the source window. Test case is easy, two directories, two text files in one directory. Two thunar windows for each directory. Drag one file to other directory.
It works fine here. Could be some special case, please provide more details.
Closing; Reopen with more detailed information.
This was triggered by improper installation and restart.