Components non-free and contrib are not enabled after installing to virtualbox virtual machine.

[jds1307@telenet.be]

I downloaded and installed the latest Debian CD image (http://cdimage.debian.org/debian-cd/8.3.0/amd64/iso-cd/debian-8.3.0-amd64-CD-1.iso)

Installing to bare metal enables the components main contrib and non-free.

Installing to a virtualbox virtual machine only enables the main component, not contrib nor non-free.

Why is that?

Is it intended behaviour? If so, what is the reasoning behind it?

Is it a bug?

I did some debugging and the problem seems to be located in the installers 'apt-setup' package.
In that shell script the calls to 


db-get apt-setup/non-free

and 

db-fget apt-setup/contrib

return false when installing to virtual machine, but they return true when installing to bare metal.

Is there a way  to set up debconf so that it enables components contrib and non-free when installing to 
a virtualbox virtual machine?

Any advice gratefully received,

jds1307