Ubuntu 9.10: switch in KVM, mouse is detected but not usable immediately

Ubuntu 9.10: switch in KVM, mouse is detected but not usable immediately

I use a KVM switch to jump between my tower and laptop, both placed on my desk. With Ubuntu 9.04 this worked perfectly. In 9.10, when I switch to the tower, then back to the laptop, the mouse is detected (as shown by /var/log/messages) but moving it has no effect. If I use Ctrl-Alt-F1 to switch to the TTY, then Alt-F7 back to Xorg, the mouse starts working.