mounting a directory on a container fails if not the default user is used

I’m trying to mount a directory inside a image but it fails if I create another user.

I use the following Dockerfile:

RUN NET USER mynewuser /add
RUN NET LOCALGROUP Administrators /add mynewuser
USER mynewuser

After building the container I run it with docker run -it --rm -v ${PWD}:C:data containername.
But when I try to cd into the data folder I get the following error:

C:>cd data
Access is denied.

When I use the powershell inside the container I can cd into the data folder but a dir command fails:

PS C:> cd data
PS C:data> dir
dir : Access to the path 'C:data' is denied.
At line:1 char:1
+ dir
+ ~~~
    + CategoryInfo          : PermissionDenied: (C:data:String) [Get-ChildItem], UnauthorizedAccessException
    + FullyQualifiedErrorId : DirUnauthorizedAccessError,Microsoft.PowerShell.Commands.GetChildItemCommand

When using the image, everything works fine as well as with the container.

Do I need to set permissions for the user even though the new user should already have administrator rights or is it a bug of the image?

Source: StackOverflow