Problem environment: HP Probook with i5/4G memory using mouse pad. Windows 8 Pro, Virtualbox 4.2.12, extension 4.2.12.
Before installing Virtualbox with extensions, mouse works OK.
Install Virtualbox and extensions and mouse frequently freezes - like the old ball mice when the roller grips started failing - most frustrating.
(Same problem does not occur on newly installed W8 desktop)
After re-installing operating system, mouse worked OK, install Virtualbox and problem reappears.
Uninstall does not fix problem.