title: Why does `vagrant up` cause the VirtualBox VM window to appear?
body: <p>After following the vagrant tutorial everything seems to be going fine. However something new and slightly annoying has started happening when I run <code>vagrant up</code>: VirtualBox also starts up and I see a VM window which seems to correspond to the Vagrant VM open. I've used Vagrant many times in the past without this happening, and IIRC <em>even for this current vm that I'm using</em> VirtualBox wouldn't necessarily open just because I ran <code>vagrant up</code>.</p>
  
  <p>What is causing this? Why does <code>vagrant up</code> cause the VirtualBox VM window to appear? (and steal focus from my Mac OS X Terminal window, which is quite annoying)</p>
  
  <p>Note: The answer in my case is <em>not</em> that Vagrant uses VirtualBox. If this were the case then VirtualBox would have always been opening in the background and I'm quite sure this is a new behaviour.</p>