Keyboard button mapping reverts to original setting after reboot

I have a Logitech Y-ST39 Internet keyboard that works fine; it has seven assigned extra function buttons across the top of the board (Search, Files, E-Mail, WWW, Mute, - and + volume) but I've noticed that the one of them, WWW, keeps giving me the "Files" function instead of the Internet.
I've successfully re-set this several times in the Control Panel, so that all works fine, but, on rebooting, the same problem returns. as if I'd made no correction at all.
I have Windows XP Home Edition, and all other hardware (and software) works fine.
Is there something I can activate to permanently set the changes I make?
Maybe Control Panel/ keyboard is not the right place to set changes...
The keyboard obviously came with the PC and doesn't have a separate software CD so I've unplugged and re-plugged so that it detects and installs the hardware drivers just to make sure they're the right ones, but to no avail. Everything else on the keyboard works well.

 

Thanks for this suggestion.
I loaded the software and updated the Keyboard driver, but that fault persists.
I also noticed that there are several drivers to choose from in the device driver manual installation option, but all of them seem to have the same problem.

As I indicated in the initial posting, I can remedy the fault quite easily in any session, but as soon as I reboot, it's back to square one. Very odd.

 

By using a bit of lateral thinking, I have found a solution to this baffling problem, though not a cause for it.
When the WWW button opens Files, the path is C:\Windows\Program Files\Internet where there are some files associated with my current ISP, but which are not in use. By moving this folder into another (Internet Explorer), the WWW button can no longer find the folder it seeks, so its function has apparently reverted to opening the web browser as it should do.
Why it started doing that in the first place is still a mystery.