DHCP server implementation

I have implemented a DHCP server on my network with a span of ten addresses. Only seven computers are configured to obtain their IP addresse by DHCP.
When I check the DHCP mangement interface on the server I notice that invariably one station has taken 4 IP addresses. Of the 4 lines assigned to the same station one shows a normal client icon (i.e. a screen+keyboard) the three other lines have icons representing a screen+keyboard+phone.
Can someone tell me why this is happening?

Thank you