key binding with virtual box inconsistent

I'm not sure if this is a unity or virtualbox issue, exactly, but based on a vbox ticket (below) I think it's unity.

when keyboard/mouse are grabbed in a windows guest OS, pressing the "windows key" opens both the start menu in the guest and the Dash on the host, stealing focus from the guest. Pressing again closes the dash and returns focus.

however, other key bindings, just as ctrl+alt+arrows do not get processed on the host until the guest is un-grabbed. my understanding is that his is how it should be, and windows key should not be processed on the host too, based on this vbox ticket: https://www.virtualbox.org/ticket/1066

what's causing the windows key to be able to over-ride the grab, and can it be prevented?

additionally, can it be conditional, where it only does so when the mouse is outside the vbox window? and if so, can that fix work with all other hotkeys bindings?

This is in 12.04 LTS amd64 that was upgraded from 10.04. vbox was installed after the upgrade and had not been used before.