It appears to be an issue with your setup

I tried it on both my live aswell as development setup both without issues as serveradmin or reseller

I'm however not sure how to go around to troubleshoot this issue.

Did you try this with Chrome or Firefox, do an iisreset and make sure the browser cache is cleared?

i assume the files are fine (as it is pretty straight forward to copy them)

other option could be database procedures or similar.