Need to convince xFi to apply a port forward to device's current address

I've been having problems for the past few days in getting a port (Port 21 -- the FTP port) to forward to a Network Attached Storage (NAS) device that I have on my home network.  Some time ago I had set the static IP of the NAS to 10.0.0.253, which is at the very top of the DHCP addressing range.  After reading some xFi forum posts, I concluded that I needed to move that static IP down into the midst of the DHCP ranges to get forwarding to work, so I moved the NAS' IP down to 10.0.0.241.

 

Most everything is cool.

• The router (both xFi interface and 10.0.0.1 Web UI) shows the IP as being 10.0.0.241.
• I can ping 10.0.0.241 and get a return.
• I can use an FTP client to see the desired NAS folders, at 10.0.0.241:21.

HOWEVER...

When I use the xFi interface to forward the port from the Gateway's Internet-facing address to my NAS, it forwards the port to the NAS' old IP address -- 10.0.0.253.  With the xFi UI, you forward a port by selecting the device to forward to.  So, the port forwarding software still records the NAS as being at 10.0.0.253, rather than being at 10.0.0.241.

 

Does anyone have advice regarding what I need to do to convince the xFi interface that it should be forwarding to 10.0.0.241?