Problem on deleting client on DHCP Server

[hansz]

Hi..I have a confuse problem. On services: DHCP Server I added a client by registering it's MAC address, then I remove this client. On the list it's looked like it's already deleted, but strangely when I check on status: captive portal, I saw this client still can access. How can this be?? as addition in service: DHCP Server I have already marked "Deny unknown clients".