Update on this issue. I have at least pinpointed it.
With Windows 8 guest running under Workstation 9.0.1 on Linux x64, and with Viewsonic TouchPanel,
if you 'connect' the Touchpanel to the running guest use it, then disconnect the touchpanel (using VM>RemovableDevices) you will
end up with a mouse pointer in Windows 8 that acts like either the left or right mouse button is continually
depressed. Only solution is rebooting the Linux host to restore normal mousing inside of Workstation.
It does not matter which VM you open, after the mouse problem is initiated, it affects all VM's until the Linux
host is rebooted.
The TouchPanel shows in removable devices as Quanta OpticalTouchScreen
Viewsonic's model number is VS14833