> It is quite sure that only the disklabel disappears, I have never observed any
> damage to neither the Risc OS nor the RiscBSD partitions.

  When I run disklabel, I get a  

non-adfs offset = 0006e110
RiscBSD partition @ 0006e110

error message from it (I.e. in stderr)
  
   When I partitioned my disk I used the 'clear' button to get me a 220.1MB 
RiscOS partition. This informed me that...

   Start of non RO area   450832
   length on non RO area  224651

  This is in sectors (512bytes on my disk and yours)

To get this into cylinders, divide by sectors/track*tracks/cylinder=576 
(96*6)

  Anyway, you should get a 
non-adfs offset = 0001FB18
RiscBSD partition @ 0001FB18
message from disklabel.   

and the cumana software should say that your non RO area starts at 1290816

  
  Hope this is of help!

Ale.