Ubuntu 12.04 32bit / Virtualbox 4.1.12

I'm at my wit's end with an issue I have with with multiple Virtualbox windows run fullscreen under Unity. When I click the Virtualbox icon on the Dash, the last-accessed Virtualbox window opens. That's fine if that's the VM I want to work with but not so if I want to work with another since the open VB window prevents me from clicking the Dash icon and so I can't bring up the 'window selector'.

Is there a setting I've missed or some other way to let me switch to the window I want without needing to close down the last-used virtual machine?

TIA,

Geoff