Why Are Icons Lost After Upgrade?

[Jasper Huijsmans]

Rich Shepard wrote:
>    I've upgraded a couple of hosts here from 4.0.6 -> 4.2.1. The icons on the
> panel are lost when this happens. Why? I'd like to make that file read only
> so it's not trashed on the upgrade. That would save me a lot of time.
> 

What exactly is lost? Launcher configuration or icon themes? The icon 
themes were changed between 4.0 and 4.2.

	Jasper