1.To isolate the problem remove cisco clean access agent from the desktop.
2. Remove the port security from this port.
3.Use "clear mac-address-table dynamic" on both switches.
4.Now again check , whether same MAC address is learning on both switches.
5.If still it is learning on the port of the switch, where it is not suppose to learn then shut that port.
6.Now see whether it is learning on both switches or it is learning on the actual switch.
7.If it is learning on the actual switch, then definitely the host connected on other port on switch has malicious actvity going on.check that host.
HTH..rate if helpful...