How can I delete a device that isn't there?

Here's what's going on... when I am setting up port forwarding (and I know how to do it, and have disabled Advanced Security), I am choosing a device with the IP of 10.0.0.150 which has a name of Household's Linksys Router. When I have finished and saved the port forwarding settings, it shows the settings have been applied to "No Associated Device" which has an IP address of 10.0.0.101. There is only one device connected directly to the Xfinity modem, and that is the aforementioned Linksys Router at IP 10.0.0.150. I have even had Xfinity 'forget' all devices that have connected to the modem in the past. I can find no way to change this and get it to apply to the correct IP address, so all of my port forwards are broken currently, which means my personal media server, music server, game servers etc. are inaccessible outside my network. How can I fix this if your cloud is going to continue applying a setting incorrectly?!?

I have to say, moving this functionality to the cloud was one of the stupidest things Comcast has done with their routers. Half the time, your servers can't even talk to my modem in order to even delete a setting such as a port forward, whereas when it was all done locally on the device, it always worked exactly as intended and worked every time. It was not even a good idea to move this functionality to the cloud, which makes it all the more amazing that it made it through any discussion to actually see fruition! Please move it back to the modems, so we can have some control back.