On an Ultra1 with sources as of this afternoon, I see this when trying
to boot netbsd:

Sun Ultra 1 UPA/SBus (UltraSPARC 167MHz), No Keyboard
OpenBoot 3.11, 320 MB memory installed, Serial #8141395.
Ethernet address 8:0:20:7c:3a:53, Host ID: 807c3a53.



Rebooting with command: boot
Boot device: disk  File and args:
NetBSD IEEE 1275 Bootblock
>> NetBSD/sparc64 OpenFirmware Boot, Revision 1.9
>> (erik@medja.h.erikb.net, Sat Jun 17 22:25:15 CEST 2006)
Failed to load 'netbsd'.
: trying netbsd.gz...
open netbsd.gz: No such file or directory
Failed to load 'netbsd.gz'.
: trying netbsd.old...
open netbsd.old: No such file or directory
Failed to load 'netbsd.old'.
: trying netbsd.old.gz...
open netbsd.old.gz: No such file or directory
Failed to load 'netbsd.old.gz'.
: trying onetbsd...
Memory Address not Aligned
ok


The previous working kernel was 4.99.22 from 7th of July.

regards
- Erik