My STBs were like that forever. Older Actiontec Rev A router. The only time you need them to be active is for the Remote DVR or HM-DVR functions, and during guide updates. If you have the channel guide updating and do not use the mentioned features I would not worry. My router would not show the STBs active even after a factory reset of the router, and Remote DVR would not work. So I was shipped a new router. Now my connections show active. You can try a factory reset. But like I said, if you are not having trouble I would not worry about it.
Device Name: IP-STB1 Connection Type: Coax IP Address: 192.168.1.103 Status: Active
Device Name: IP-STB2 Connection Type: Coax IP Address: 192.168.1.101 Status: Active
Device Name: IP-STB3 Connection Type: Coax IP Address: 192.168.1.102 Status: Active