Can not exactly say there is a issue with CP. When you disconnect lan and attach only laptop obviously only laptop is sending a traffic. While with LAN other hosts are pumping the traffic. TO confirm use cpview and under CPU -> Top Connections see who is transferring the data.
Plus if you feel hosts are sending a data and no getting proper bw; capture the packet using tcpdump on your internal interface or external inteface for a min or so and then analyze it with cpmonitor.
Thanks and Regards,
Blason R
CCSA,CCSE,CCCS