If your remote is only controlling your tv volume and not the decoder, hold OK and -V for 3 seconds untill it flashes red twice, then it should be back to controlling decoder volume... also the reverse applies, if you want to switch to tv volume control, hold OK and +V for 3 seconds untill it...
This is some sort of glitch in the firmware yet to be fixed... you can reboot until the cows come home, but after a reboot or any other event where the decoder comes back on from a power cut etc, it will have this issue for atleast an hour or so, then it just dissapears....