I realise that this is a duplicate of this post but I was unable to comment on that one.
I am able to replicate this issue on a fresh install of 13.04
I have tried installing the prop nvidia drivers, this had no effect
I then put Cinnamon and KDE on to see what would happen. Neither desktop had this issue, it only happens with Unity. The area clipped seems to be exactly the same size as the footer of the guest in a normal window.
This clipping only occurs in seamless mode. And only effects the guests windows (Windows 7). A window from the host (Ubuntu 13.04) renders correctly to the bottom of the screen.
I have tried different resolutions on both the host and the guest, no effect.
Does anyone have any suggestions?
EDIT: Also if I move the mouse near the bottom of the screen it sort of scrolls down to show the clipped off bit. This was noted in the other post but what is interesting is that the visible part of each open window also scrolls. I mean that if you have a command prompt open and you move you mouse to the bottom of the screen the menu bar at the top disappears and an equal area of the guests desktop is revealed at the bottom.
EDIT: If I plug a second screen into the laptop and apply the display changes, the problem goes away. But if I then reboot the VM it bluescreens on boot until I unplug the second screen and reboot....