The point of this hint IS explained in the hint. But maybe you need to experience the problem before you understand it.

To recap on the problem - if you have a Logitech UK keyboard it doesn't have the exact same layout as a standard Apple UK keyboard. The fix for that is to install the Logitech Control Center software which installs a new keyboard layout into the OS. The problem with this is that if you switch to using this layout, for some bizarre reason the OS insists on switching back to an Apple layout after a seemingly random period of time (for the life of me I can't work out what triggers this - it just seems to happen when it feels like it).

I have tried disabling the non-Logitech layouts in the International->Input menu pane of SysPrefs, but you are not able to disable them all - there has to be at least one Apple-supplied layout enabled. This is the one that the OS switches back to, whichever one you leave enabled. I have also tried fiddling with the Input Source Options but this does not seem to affect the problem at all.

It may be that you have to be using a UK system to experience this problem, but it is extremely annoying and appears to be a bug. The hint supplied here is the only cure for the problem that I have come across, and it does work. The only concern I have is what will happen when the next OS upgrade comes along.