Mouse - Network connection = weird behav

This problem concerns a customer of mine. I do not have access to his computer, as it is owned by his company and its use is heavily restricted (he can't even access Control Panel). I work for an ISP and installed for this customer a static IP with a Zyxel cablemodem/router, which is configured to be used as a cablemodem only, because it is connected to just one client (my customer's laptop.)
The laptop is a Dell Latitude C610 with Windows XP Pro loaded, and is connected to a docking station that came with it (also from Dell). It has a Dell Ergonomic 1.2a USB Compatible Mouse that fits the docking station. All of this was set up brand new just a few days ago by his company. The drivers for it are installed, according to the customer. Thecustomer called me and said that his mouse was jumping all over the place and that his own tech support had not been able to figure out why - they even dial-accessed into his machine and looked at the configuration. He also mentioned (finally) that his cable light was blinking, which means that his Zyxel modem was not online. As far as I know, the only time I have seen this kind of mouse behavior in the past, has been when the drivers were not installed for the docking station mouse. I said that as far as I know the network connection should have nothing to do with the mouse working properly or not, but that the cable modem should be online all the time - and tried to explain how a static IP works. He *says* he didn't disconnect it, but I do know that he has disconnected it once already, and that he also shuts down and disconnects his laptop every night. I asked him to reboot the Zyxel cable modem anyway, to get it back online. It came back online immediately no problem, but, as soon as it did, and this is the weird part: his mouse began to behave normally. Since he was happy he could finally get to work again, I left it at that, but now I want to know if anyone