Oracle Virtualbox has released v4.3.16 with lots of bugs fixed and/or new items added. For Linux, a crash in Gnome session has been fixed and X.Org Server 1.16 now is supported in X11 guests.
According to the release note, the new version fixed restoring 32-bit FPU state on 64-bit capable VMs and restoring guest FPU in raw-mode VMs, properly restore normal/scale mode guest-screen size after exiting full-screen/seamless mode, fixed video recording support for 3D data regression. See the detailed changes.
How to Install / Upgrade Virtualbox 4.3.16:
Press Ctrl+Alt+T on keyboard to open the terminal. When it opens, paste the command below and run to add the official Virtualbox repository for Ubuntu 14.04:
sudo add-apt-repository "deb http://download.virtualbox.org/virtualbox/debian trusty contrib"
For Ubuntu 12.04, replace trusty with precise in the above command.
After added the PPA, get the keyring:
wget -q https://www.virtualbox.org/download/oracle_vbox.asc -O- | sudo apt-key add -
Finally install vbox 4.3:
sudo apt-get update; sudo apt-get install virtualbox-4.3
Or upgrade via Synaptic Package manager or Software Updater.