App is getting damaged when I replace it as non-administrative user

Question

Hey people,
When I want to update e.g. VLC Player, as an administrator, it is simple: I just download the dmg, mount it and drop the new version of the VLC.app into the Applications folder to replace the old VLC.app. Few days ago I created a new admin account and changed my old account  to normal user. If I want to install new software that I did not use before, everything works as expected: when I drop an .app package into the Applications folder, I need to type in the admin login and password to allow this operation, then the package will be copied and I can start the new app.
My problem:
If I want to update the software by replacing the app as non-administrative user, the system first will promt me to keep both files, replace an older one or to stop - so far so good. BUT, when I select to replace, the copying process actually begins before the administrator prompt and it results in corrupted file. I also tried to create a new user account. So then I need first to remove the broken app (admin prompt once again) and then to install the new one (3rd admin prompt).
I attached some screenshots to visualize the issue. I have the same issue on two different macs with different  user/admin names. I hope you have any idea how can it be fixed.
1. I download the package:
2. Mount the package:
3. Drag the VLC app to the Applications folder (selecting >Authenticate in the prompt)
4. Copy prompt (>Replace):
5. Authenticate with administrative user
6. Error message:
7. Corrupted file:

Answer 1

Thanks, you helped me. I had gotten hung up on '--user = <vboxuser>' in the ExecStart line, which works for one of my other services, but not this one.