interface loopback deletion panic

[Nomad Esst]

See the following. When I try do delete the loopback interface, I face this kernel panic. I'm using FreeBSD9.2 AMD64

[root at lower ~]# ifconfig lo1 deletein_scrubprefix: err=65, prefix delete failed
panic: rtfree 2
cpuid = 3
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a/frame 0xffffff809b08a620
kdb_backtrace() at kdb_backtrace+0x37/frame 0xffffff809b08a6e0
panic() at panic+0x1ce/frame 0xffffff809b08a7e0
rtfree() at rtfree+0x105/frame 0xffffff809b08a800
in_ifadownkill() at in_ifadownkill+0x115/frame 0xffffff809b08a830
rn_walktree() at rn_walktree+0x7c/frame 0xffffff809b08a860
in_ifadown() at in_ifadown+0xbe/frame 0xffffff809b08a8b0
in_control() at in_control+0xa31/frame 0xffffff809b08a960
ifioctl() at ifioctl+0x803/frame 0xffffff809b08aa60
kern_ioctl() at kern_ioctl+0x106/frame 0xffffff809b08aab0
sys_ioctl() at sys_ioctl+0xfd/frame 0xffffff809b08ab10
amd64_syscall() at amd64_syscall+0x4df/frame 0xffffff809b08ac30
Xfast_syscall() at Xfast_syscall+0xf7/frame 0xffffff809b08ac30
--- syscall (54, FreeBSD ELF64, sys_ioctl), rip = 0x801170abc, rsp = 0x7fffffffd3b8, rbp = 0x7fffffffde85 ---
KDB: enter: panic
[ thread pid 16247 tid 100253 ]
Stopped at      kdb_enter+0x3b: movq    $0,0x5d0072(%rip)
Thanks in advance.