Panic in nat_inlookup (trough ip6_input)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I just experienced a panic on a 6.1/amd64 server during an ipfilter restart 
(the last thing I saw on my SSH connection was "Stopping ipfilter.":

fatal page fault in supervisor mode
trap type 6 code 0 rip ffffffff8023f2c4 cs 8 rflags 10212 cr2  1fa0 cpl 4 rsp fffffe80082c6970
kernel: page fault trap, code=0
Stopped in pid 0.3 (system) at  netbsd:nat_inlookup+0x95:	movq	0(%rax,%rdx,8),%rbx

db{0}> bt
nat_inlookup() at netbsd:nat_inlookup+0x95
fr_checknatin() at netbsd:fr_checknatin+0x119
fr_check() at netbsd:fr_check+0x3e3
pfil_run_hooks() at netbsd:pfil_run_hooks+0x9d
ip6_input() at netbsd:ip6_input+0x3d9
ip6intr() at netbsd:ip6intr+0x77
softint_dispatch() at netbsd:softint_dispatch+0x7b
DDB lost frame for netbsd:Xsoftintr+0x4f, trying 0xfffffe80082c6d70
Xsoftintr() at netbsd:Xsoftintr+0x4f
--- interrupt --
0:
db{0}> show reg
ds	1
es	0
fs	0
gs	c420
rdi	fffffe80082c6ac0
rsi	11
rbp	fffffe80082c69e0
rbx	a065dbd4
rdx	3f4
rcx	1
rax	0
r8	a05b002a
r9	11
r10	fffffe80082c6ac0
r11	bb01
r12	fffffe80f966a808
r13	5014002a
r14	a05b002a
r15	6
rip	ffffffff8023f2c4	nat_inlookup+0x95
cs	8
rflags	10212
rsp	fffffe80082c6970
ss	10
netbsd:nat_inlookup+0x95:	movq	0(%rax,%rdx,8),%rbx

What strikes me as odd is that the call chain seems to state that NAT is called on IPv6 input.