Anyone seen this panic?

A relatively CURRENT kernel from:
FreeBSD kobe 7.0-CURRENT FreeBSD 7.0-CURRENT #0: Sun Sep  2 03:46:34 EEST 2007

just panicked on me with the following backtrace:

(kgdb) bt
#0  doadump () at pcpu.h:195
#1  0xc05bcb0e in boot (howto=260) at /home/build/src/sys/kern/kern_shutdown.c:409
#2  0xc05bcdcb in panic (fmt=Variable "fmt" is not available.
) at /home/build/src/sys/kern/kern_shutdown.c:563
#3  0xc081bfb3 in trap_fatal (frame=0xd5e8f934, eva=3216998400) at /home/build/src/sys/i386/i386/trap.c:872
#4  0xc081c890 in trap (frame=0xd5e8f934) at /home/build/src/sys/i386/i386/trap.c:277
#5  0xc08026eb in calltrap () at /home/build/src/sys/i386/i386/exception.s:139
#6  0xc0819e4c in slow_copyout () at /home/build/src/sys/i386/i386/support.s:772
Previous frame inner to this frame (corrupt stack?)
(kgdb)

Does this look familiar to anyone?

Line 772 of support.s is here:

 767 #if defined(I586_CPU) && defined(DEV_NPX)
 768         ALIGN_TEXT
 769 slow_copyout:
 770 #endif
 771         shrl    $2,%ecx
 772         cld
 773         rep
 774         movsl
 775         movb    %bl,%cl
 776         andb    $3,%cl
 777         rep
 778         movsb