The folder probably has a desktop.ini hidden inside which changes the name that is displayed for it. When you start to copy the folder, you see its real name. When the desktop.ini file is copied over it changes the name that you see.
You can turn off localized names in Preferences if you always want to see the real names, but it may change the names of several system folders to ones you aren't used to.
In Explorer duplicating the folders take 1-2 seconds and they get the same name (without 'Copy' though).
Pls see screenshot '5' above and compare with the latest one (7)
My experience is that in most cases (but not always) Opus only refreshes after changing folders, i.e. temporarily switch to another folder and then return.
There is a desktop.ini in the folder, I viewed the contents, it says
Many thanks Leo. That solved the matter.
BTW in my case I needed to rebootmy pc, so as to 'clear' things though: Opus File->Exit and relaunch would open the last 3-4 sessions (repeatedly).
Anyway, it is fine now.