When I hit the okay button, and browse up and down (what's on now and next) it will randomly jump to channel 5. I've refreshed the remote batteries, tried different controllers, even different boxes. I can only conclude it's some sort of software problem.

Has anyone else noticed this?

I haven't noticed that problem, but agree that it sounds like software. If you're not aware already, you can force a software update on the Media box:

(i) Pull out the power cable from the back of the box (or power it off at the mains - whatever is easiest).
(ii) With power off, press the left and right arrow keys on the front of the box, and keep them held down.
(iii) Plug the power back in, keeping the arrows keys pressed until the box 'boots'.

If a software update is available, it will download and install it. If there's not, the box will just boot as normal. By the way, you can release the arrow keys once the update starts.

I forced an update a couple of weeks ago, and it changed the look of the menus, and some other things. The version of code I currently have is 3.5.0.023 (HD Media Box). You can see what version you're running by accessing 'diagnostics' from the settings menu.

I have an HD box, but the software update procedure is the same for the 'non-HD' box.

Good Luck!

It's a Thompson DVR on version 3.2.2.3 but won't go any higher when trying the update process.. I'll raise it with UPC and see what they say. Thanks for your advice