I'm using 4.99.25 on amd64, updated as of ~1hr ago.
I'm using GENERIC.MP built with LOCKDEBUG and DIAGNOSTIC.
Unfortunately, I don't have any more information because I thought
"oh, it'll be in the message buffer" (I use DDB_TEE_MSGBUF=1).  Well,
it's pretty obvious that syslogd wasn't running--as would be expected.
 I'll do a shutdown again and try to capture it somehow (there's
always a pencil and paper!).  Can anyone else running amd64-current
reproduce this?  Someone with a serial console or digital camera might
have an easier time than me recording it down, as it filled the
screen. ;)

Regards,

--Blair