For years I've been using a Belkin Omnia KVM to switch my mouse, keyboard and monitor between to Linux/x86 hosts.
When Debian introduced the X ''evdev'' driver, I started having troubles. Each time I switched from one machine to another, the mouse pointer would behave oddly, leaping about all over the place.
This turns out to be because the Belkin is losing track of the protocol the mouse is using to talk, and it's not until the driver works out something is wrong and resets than sanity is restored.
The solution that works for me? Set the protocol at evdev load time, on both machines. Add a file psmouse.conf to /etc/modprobe.d on both machines. psmouse.conf contains
options psmouse proto=imps resetafter=2
This fixes the protocol to ImPS/2 and forces a reset after just two strange packets from the mouse. And my mouse no longer goes bonkers after switching the screen.