SMB session from MobyLinuxVM times out after 15 minutes

When I start Docker and immediately run a container using a volume mount, ie

C:\> docker run -it --rm -v c:/users:/users ubuntu bash

the mount is available under /users. But after 15 minutes idle time the session is lost, and in the container I get

root@47679acbead6:/# ls /users
ls: cannot access '/users': Permission denied

If I open Shared Drives in the Docker settings and remove and then readd C then the mount is reestablished.

If I start Docker and wait for half an hour and then attempt to run a container as above I get this behaviour:

$ docker run -it --rm -v c:/users:/users ubuntu bash
C:\Program Files\Docker\Docker\Resources\bin\docker.exe: Error response from daemon: oci runtime error: container_linux.go:262: starting container process caused "process_linux.go:339: container init caused \"rootfs_linux.go:57: mounting \\\"/c/users\\\" to rootfs \\\"/var/lib/docker/overlay2/cf0a843aa74b531b582bc78bfa2b0134e98caed73f13beedb206fb6f2f53cae5/merged\\\" at \\\"/users\\\" caused \\\"stat /c/users: permission denied\\\"\"".

I have attempted to increase the SMB idle session timeout on the host using NET CONFIG SERVER /AUTODISCONNECT:1440 (and restarting the host), but the SMB sessions from MobyLinuxVM still time out after 15 minutes.

I see nothing in the Docker log that seems related to this problem. I have searched the forums and the issue tracker for problems resembling mine, but without any luck.

I am running Docker version 17.06.2-ce, build cec0b72 on Windows 10 Pro 1703/15063.608 - but this behaviour has been present on this PC for the past couple of Windows and Docker releases.

Any help would be appreciated.