I presume the reported problems are that some older boxes and DTVs are unable to be retuned and some boxes (such as my own Philips DTR1500) are difficult to retune.
Incidentally, if anyone has the same problem I did (rescanning the channels didn't pick up the new 5 location), you need to do a factory reset.
The procedure for this is not too fiddly.
- unplug the box from the mains
- While holding the + button on the front of the box, turn the box on. The red LED will light. After a few seconds, the Multicolour LED will turn orange/yellow. Eventually it will flash. Hold the + button until it flashes.
- Press the + button again and the Multicolour LED will start to flash red.
- When the LED flashes red, enter the code 9900 on the remote. If the code is accepted, the multicolour LED will flash green a few times. If it doesn't, re-enter the code.
- Wait, and in a few minutes, the box will reboot itself and start the installation wizard.