Q: finder opens local volume using smb

Since 2 days Finder treats my desktop as a server and forces me to provide my account and password for a locally attached volume (see picture) that's already open on the desktop. After it's opened for the 2nd time the volume shows as smb-mounted (see picture of both volumes next to each other)

I am using MacOS Sierra since the beginning of October. The problem only occurs with my normal account -- my second (admin) account doesn't show the same behaviour. I have deleted the Finder and Sidebar plist preferences without success. I have also rerun the Sierra installer without success.

I'm also using Path Finder as a Finder alternative without problems. Removing the login window is only possible via Fore-quitting the Finder.

Any suggestions other than reinstall from Time Machine.