You misunderstand me. Perhaps I wasn't clear enough. As the experiment is carried out, to be clearer.
It opens a Nemo window,
use F3 or new tab to open a window with large file for copying
copy the file
wait till mint says its finished
... (it hasn't really because the copy speed is shown as 200Mbps+
.... buts really only about 7Mbps over USB2 to my transcend usbs)
wait a few seconds for generosity
select eject from the nemo menus
it ejects (and the subwindow showing the usb disappears)
If you then remove the USB (while you know the copy must still be continuing at 7Mbps) then the file will be corrupted.
Nemo reports the copy finished
Nemo reports the usb unmounted/ejected (by closing the window)
It HAS NOT FINISHED
If you use SpaceFM then it will still report the copy being finished early (simply because Linux reports it thus to the application) but the difference is that if you select Remove/Eject it will either:
a) close the window immediately if there are no operations still in progress; or
b) show a sub window with the "eject progress" at 50% until all operations have finished then close all related windows when it has finished.
Although SpaceFM has some nice features and does eject USBs correctly I like what the team is doing with Mint and would like to stay true to its Core applications if possible. So I'd appreciate either a suggestion of changes to my configuration so that nemo behaves correctly or perhaps acknowledgement of the issue and the possibility of a fix.