Docker folder permissions changed

Hi,
I'm using PGAdmin to manage my postgres databases and just discovered a bit strange behavior - every time when container is recreated (due to upgrade) or docker service is restarted (this is really interesting) - permissions of the folder are "Reseted". This is an issue because I want to backup the folder of docker and as I'm running containers without root access - this is an issue. Workaround that I tried to perform is after initial creation of container - to add additional ACLs that grant read / write permissions to docker use - and then - my backup SW (running again in container) can backup data and when it's necessary - to restore it.
The problem is that every time when docker service is restarted - permissions are restored and backup is not working.
Also it will be very good if it's possible to run container with "custom" user.

Start by reproducing the permission reset described for the pgAdmin Docker container when the container is recreated or the Docker service restarts. Compare the folder permissions before and after those events, including the reported custom-user and ACL workarounds; done means the permissions needed for backup remain usable after restart or the supported user configuration is clearly defined.