Beige G3 SCSI disk install problem

[Bernhard Prümmer <Bernhard.Pruemmer%Vodafone.DE@localhost>]

Hello there,

I have problems installing NetBSD 4.0.1 on my Beige G3 (OF 2.0f1)  
using an internally attached IBM SCSI disk DDRS-39130.
It is not an item of bus termination. The NetBSD installer detects the  
drive without problems.
Partioning and formatting of partitions also works.
But then, when sysinst runs the command

        /usr/sbin/installboot /dev/sd1a /usr/mdec/bootxx /boot

it fails and tells me that the file system is *read-only*.
The workaround I have found is to finish installation (packages are  
installed without further problems),
and then get back to the command line, run

        /sbin/mount -u -w /

followed by the installboot command above.
The disk will be bootable but not know about the boot device (sd1 in  
this case), and hence
NetBSD asks for it every time the system is booted.

Now, why the heck does the installboot command fail in the first  
place, though package installation works?
Any hints are welcome.

Cheers
Bernhard