Gitea as Win Service -> Files get wrong owner

I have a Gitea 1.13.0 running on a Windows 2012 RC 2 (no influence on that, sorry). The service is configured to run as a domain user DU. It runs well.

Problem: As soon as I adopt an existing repository owned by DU new files are owned by Administrators instead of DU. This leads to conflicts.

I created the service as writen in the Gitea docs as well as with nssm, both with user DU set as Log on as without.