Any VirtualBox newer than 4.3.14 causes Aero UI elements to flicker or slow / not redraw when the mouse hovers over them when 3D support is enabled and the 3D driver is installed.
It has been noted that using a video driver other than the binary driver stops the flickering.
This has been seen on 340.xx series. Unsure if it is a VBox bug or NVIDIA bug.
VirtualBox bug: https://www.virtualbox.org/ticket/13653