I have the same problem, but with a completely different set-up... I have two LC 475s sharing a keyboard and mouse with a KVM switch. Whenever I switch between computers the keyboard stops working, but the mouse works fine. As in your case, disconnecting and reconnecting the cable solves the problem. I've tried several keyboard/cable combos, so it's definitely an issue with the KVM, but I always thought it was odd that the mouse was not affected.

Sorry, that's not much help...