I recently installed Ubuntu 13.04 and Virtualbox 4.2.10-dfsg-0ubuntu2 with guest extensions installed and my Windows7 guests running in Seamless mode have the bottom part chopped off. The Windows Start button is slightly taller so it peaks out from below and that visible bit is clickable. This did not occur in 12.04.
It seems like the Virtualbox seamless boundaries end too high up (perhaps they start at the top behind the Ubuntu top panel) and the boundaries are not in sync with the Windows guest, or else the Windows Start menu/taskbar would also just appear higher up and not chopped off at the bottom of the screen.
I have tried enabling the 3D Acceleration Mode for the vm but that didn't help.
EDIT:
- I am running the proprietary Nvidia graphics drivers (nvidia-310 310.44-0ubuntu2)
- I have disabled the global menu
- I am using sloppy mouse focus
I will try to put this back to stock Ubuntu 13.04 and see if that fixes the problem.
UPDATE:
Restoring global menus did not fix the problem.
UPDATE (2013-05-02):
I was resizing the window of a program running in the Windows7 guest and when my mouse cursor hit the bottom of the screen, it seems the entire guest desktop pans down. But this left things less usable so I had to restart the guest vm. I suspect this has something to do with the interaction between Unity's top panel and Virtualbox since the effected parts are the height of the top panel.
Best Answer
I had essentially the opposite problem, windows host and a Ubuntu 13.03 guest. However the resolution to my problem may be what you need as well- perhaps setting the resolution this way on your Ubuntu host will solve the problem with your windows guest:
Screen Resolution issue on Ubuntu 13.04 installed under Virtualbox