Contents of volume bound to host not visible to other containers

Issue type: Possible bug
OS Version/build: Windows 10
App version: Docker 1.12.1-stable
Steps to reproduce:
Using Docker-compose, I have some Debian containers (running Apache/PHP/Wordpress) with volumes bound to my host (Windows 10, Docker 1.12.1-stable). Within those containers, using bash I can see files that are in a volume bound to my host (i.e. they appear with an ls command and I can edit them in nano, etc). I am using NFS in another Debian container to connect to the Wordpress containers to see files via bash, which works fine, except for the folders which are volumes bound to my host, which appear empty. Note I am using external_links to allow the containers to see each other and a common network - I don’t believe there is a problem with that, as connectivity all works fine, as does NFS, except for the volumes bound to my host being empty from the remote containers.

I presume this is a bug/quirk rather than intended behaviour?