I have spotted a bug with the tether app.
I have a device on the network with two network connections, ie Lan connection and Wifi connection. They obviously have different mac address but from the TP-Link device they have the same hostname.
If I add both network interfaces under the parental controls via the web browser, I can control each interface (parental control) settings independently. However when i now try and use the tether app, this device is now duplicated and can only control one interface. Also I get other duplicate entries of other devices even when they only have one interface.
It seems to be an issue on the tether app that does not like devices with the same hostname yet different mac addresses.