sysinst dumps core when that part of the install comes around which asks 
for a name for the disk.  It looks something like this:

Please enter a name for your netbsd disk [blah    ]:

It's normally initialised to "mydisk".

If there's already a name, it dumps core.  The name it gets if there's 
no name seems to be the make/model of the disk.  On my system with a 
Seagate disk it gets set to STxxxxxx.  If there's no name it seems to 
be OK.

I've looked through the sources but I can't find the code responsible 
for the core dump.  It could be the function savenewlabel.

Any ideas?  I might have to save the core image and do a post-mortem 
examination...

James