bwn(4) panic

`pciconf -lv` (if_bwn unloaded to prevent panic)
none1@pci0:3:0:0:       class=0x028000 card=0x000c1028 chip=0x431514e4 rev=0x01 hdr=0x00
    vendor     = 'Broadcom Corporation'
    device     = 'BCM4312 802.11b/g LP-PHY'

---
dmesg excerpt

Oct  5 09:04:48 slowbro kernel: bwn0: ucode fw: ucode15
Oct  5 09:04:48 slowbro kernel: bwn0: firmware version (rev 478 patch 104 date 0x8701 time 0x657)
Oct  5 09:08:43 slowbro syslogd: kernel boot file is /boot/kernel/kernel
Oct  5 09:08:43 slowbro kernel: panic: Duplicate free of 0xfffff8002a9c6800 from zone 0xfffff80002ae3900(mbuf_packet) slab 0xfffff8002a9c6f90(8)
Oct  5 09:08:43 slowbro kernel:
Oct  5 09:08:43 slowbro kernel: cpuid = 0
Oct  5 09:08:43 slowbro kernel: KDB: stack backtrace:
Oct  5 09:08:43 slowbro kernel: db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00baae5860
Oct  5 09:08:43 slowbro kernel: vpanic() at vpanic+0x182/frame 0xfffffe00baae58e0
Oct  5 09:08:43 slowbro kernel: panic() at panic+0x43/frame 0xfffffe00baae5940
Oct  5 09:08:43 slowbro kernel: uma_dbg_free() at uma_dbg_free+0xee/frame 0xfffffe00baae5970
Oct  5 09:08:43 slowbro kernel: uma_zfree_arg() at uma_zfree_arg+0x64/frame 0xfffffe00baae59c0
Oct  5 09:08:43 slowbro kernel: mb_free_ext() at mb_free_ext+0x185/frame 0xfffffe00baae59f0
Oct  5 09:08:43 slowbro kernel: m_freem() at m_freem+0x38/frame 0xfffffe00baae5a10
Oct  5 09:08:43 slowbro kernel: bwn_start() at bwn_start+0x16d/frame 0xfffffe00baae5a50
Oct  5 09:08:43 slowbro kernel: bwn_intrtask() at bwn_intrtask+0x1fb1/frame 0xfffffe00baae5b20
Oct  5 09:08:43 slowbro kernel: taskqueue_run_locked() at taskqueue_run_locked+0x13c/frame 0xfffffe00baae5b80
Oct  5 09:08:43 slowbro kernel: taskqueue_thread_loop() at taskqueue_thread_loop+0x88/frame 0xfffffe00baae5bb0
Oct  5 09:08:43 slowbro kernel: fork_exit() at fork_exit+0x84/frame 0xfffffe00baae5bf0
Oct  5 09:08:43 slowbro kernel: fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00baae5bf0
Oct  5 09:08:43 slowbro kernel: --- trap 0, rip = 0, rsp = 0, rbp = 0 ---
Oct  5 09:08:43 slowbro kernel: KDB: enter: panic