My Tether wasn't working for me so I decided to just enable USB tethering by hand ("usbnet enable", "iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE", etc)... Everything works just as it should with one problem: Whenever I enable IP forwarding (via "sysctl -w net.ipv4.ip_forward=1") it turns back off after a while. So I'll be surfing the web or something and then out of the blue all my packets just stop being forwarded.

I suspect that there's some sort of system process or java service running in the background that keeps disabling IP forwarding. Does anyone know what's causing this?