Here's an Ubuntu 14.04 Vagrantfile

This should fix vbguest issues in bug-1001567 as well.
I can see where a name conflict might have occurred: the namespace for config.vm.box is global across an entire host machine. So, if you've downloaded a box and called it "ubuntu/trusty64" for one project, another project will say "Ah, that box is already downloaded" and proceed to clone from it. It so happens that "ubuntu/trusry64" is the canonical name of this box from the Vagrant Cloud: https://vagrantcloud.com/ubuntu/boxes/trusty64. So I could see you vagrant upping one project that uses that name but a custom URL (like DXR does) and then vagrant upping a second project that was assuming the Vagrant Cloud image and having it be surprised. However, if you're seeing files from one project on the VM for another, I have no idea what's going on.

I bet we could leave out the URL and just say ubuntu/trusty64 here, and it would default to Vagrant Cloud and work fine.