panic in devstat_remove_entry

I've found a way to panic 5.2-BETA which I can trigger in two ways.
The first is to get an audio cdrom recognised and the corresponding
/dev/acd0tX nodes created, then replace that cdrom with one with a
standard ISO9660 filesystem.  Upon cat'ing the cdrom, the system panics.
The second way I triggered when I accidentally tried to mount an ISO9660
filesystem as UDF - with the CD in the CDRW drive, the system generates
the same panic as the first.   I've tried, without success, to get a
crash dump to get more information - gdb refuses to load the vmcore.X
file, with a 'vmcore.0: Unknown error: 0' message.  I've attached a 
transcript of the session which produced the panic.  
The kernel and world were compiled with -O
-march=athlon-xp, uname "FreeBSD buffy.brucec.backnet 5.2-BETA FreeBSD
5.2-BETA #0: Fri Dec 5 01:57:14 GMT 2003 bruce_at_buffy.brucec.backnet:
/usr/obj/usr/src/sys/MYKERNEL  i386" - it was cvsupped and 
rebuilt on Thu 4th Dec.   If there's any other information needed, I
can trigger this on demand so can get further data, and have the full
transcript of the serial session available.

--
Bruce Cran