In message <9609131554.ZM20641@physig4.ph.kcl.ac.uk> you wrote:

> Hmm some how this sounds as if the disklabel is overlapping the swap
> partition.

This can also hardly be true as the sequence (as usual if the standard
installation skript is used) of my RiscBSD partitions is root-swap-usr
and the disklabel is stored at the beginning of the RiscBSD slice, ie before
the root partition, isn't it?
It might be that the disklabel is lost every time swap space is used, at least
this would explain the rare occurence. I'll try this out.