I'm running VirtualBox 4.3.18 (and this has been happening since at least 4.3.16) on Ubuntu x64 host, with Windows 7 as a guest. Guest addons are up to date.
My host machine has 3 monitors – two external LCDs and an internal laptop LCD. The guest is only set to have a single screen.
When I go to full screen mode on monitors 2 and 1 (which are far left and right respectively), full screen mode works fine (i.e. it stays within the bounds of that monitor). When I move to monitor 3 (middle), the guest screen is stretched across the middle and right monitors. The guest resolution stays the same, I just get barn doors down the left and right. Strangely, the VirtualBox toolbar appears in the correct location on the middle screen.
Can anyone shed any light? I'd really like to get back to running 3x full screens
Best Answer
I had the exact same problem, solved it by going to the VirtualBox toolbar, View => Virtual Screen X => Use Host Screen Y