Looks like this is the problem (my PC was reinstalled a few days ago) with ownership of all files on all disks.
On the left is the newly created file - on the right side - file that already exists (this partition wasn't formatted).
Fixing the permissions (as per Lxp's post) is the best thing to do first, and always a good idea after reinstalling, as the permissions on the old drive won't usually match the account of the new install.
If the files are being moved (including removing them from the source) but you're still getting a UAC prompt afterwards, it's likely because the destination drive/folder isn't granting your (unelevated) account the right to copy/modify metadata or file permissions.
If that's the case, turning off these settings may mean the UAC prompts stop appearing:
Preferences / File Operations / Copy Attributes:
Copy security permissions
Update permissions/encryption to match the destination when moving files
The first part was executed without problem, second reporting an error.
And DOpus still causes a UAC message when moving files between different directories.
@John - I redirected only standard output, errors (if any) will still be displayed. There are a lot of files on this drive (about 10m to complete) so I wanted to hide output to speedup entire operation. You will see one line for every file so it's impossible to catch an error during displaying 100k lines.... There is no summary at the end...
Anyway, the problem was that this wasn't run from an elevated shell.
I've tried also with "icacls /set-owner <domain/user> /T" - and this also works, but doesn't go inside folders, and solutions over the internet is to use a script, set environment and variables bla bla bla...
Linux "chown" is a bit easier to use....
I tried now on another disc and I can confirm that if I only use takeown - everything works now fine. This is enough so icacls have not been used.