wpa_supplicant doesn't work with lagg

I'm having trouble using the lagg driver with wpa_supplicant.  When I
boot with this standard configuration, my wifi works fine:

> # Normal config.
> wlans_iwn0="wlan0"
> ifconfig_wlan0="WPA DHCP"
> ifconfig_em0="DHCP"

But when I boot with a lagg configuration, wpa_supplicant can't connect.

> # Lagg config.
> ifconfig_em0="up"
> ifconfig_iwn0="ether 3c:97:0e:46:70:ca"
> wlans_iwn0="wlan0"
> ifconfig_wlan0="WPA"
> cloned_interfaces="lagg0"
> ifconfig_lagg0="laggproto failover laggport em0 laggport wlan0 DHCP"

The system spends a full 5 minutes during boot trying to send DHCP
requests before finally giving up.  After boot, ifconfig shows that
wlan0 has the right ssid, but the status is 'no carrier':

> wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>         ether 3c:97:0e:46:70:ca
>         nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
>         media: IEEE 802.11 Wireless Ethernet autoselect (autoselect)
>         status: no carrier
>         ssid neural_network channel 1 (2412 MHz 11g ht/40+)
>         regdomain FCC country US authmode WPA1+WPA2/802.11i privacy ON
>         deftxkey UNDEF txpower 30 bmiss 10 scanvalid 60 protmode CTS
>         ampdulimit 8k -amsdutx amsdurx shortgi -stbc wme roaming MANUAL
>         groups: wlan

If I then manually kill wpa_supplicant and restart it with the same
command, it works fine.

> /usr/sbin/wpa_supplicant -s -B -i wlan0 -c /etc/wpa_supplicant.conf -D bsd -P /var/run/wpa_supplicant/wlan0.pid

> wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>         ether 3c:97:0e:46:70:ca
>         nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
>         media: IEEE 802.11 Wireless Ethernet MCS mode 11ng
>         status: associated
>         ssid neural_network channel 1 (2412 MHz 11g ht/40+) bssid c4:04:15:90:f5:fd
>         regdomain FCC country US authmode WPA2/802.11i privacy ON
>         deftxkey UNDEF AES-CCM 2:128-bit txpower 30 bmiss 10 scanvalid 60
>         protmode CTS ampdulimit 64k ampdudensity 8 -amsdutx amsdurx shortgi
>         -stbc wme roaming MANUAL
>         groups: wlan

/var/log/messages shows:

> Jul 28 15:22:09 mako kernel: wlan0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: wlan0: link state changed to UP
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to UP
> Jul 28 15:22:09 mako kernel: wlan0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: wlan0: link state changed to UP
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to UP
> Jul 28 15:22:09 mako kernel: wlan0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: wlan0: link state changed to UP
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to UP
> Jul 28 15:22:09 mako kernel: wlan0: link state changed to DOWN
> Jul 28 15:22:09 mako kernel: lagg0: link state changed to DOWN
> [snip]
> Jul 28 15:22:23 mako wpa_supplicant[329]: wlan0: CTRL-EVENT-SSID-REENABLED id=2 ssid="neural_network"
> Jul 28 15:22:23 mako wpa_supplicant[329]: wlan0: Trying to associate with c4:04:15:90:f5:fd (SSID='neural_network' freq=2412 MHz)
> Jul 28 15:22:23 mako kernel: wlan0: link state changed to UP
> Jul 28 15:22:23 mako kernel: lagg0: link state changed to UP
> Jul 28 15:22:23 mako wpa_supplicant[329]: wlan0: Associated with c4:04:15:90:f5:fd
> Jul 28 15:22:23 mako dhclient[533]: send_packet: No buffer space available
> Jul 28 15:22:27 mako dhclient[533]: send_packet: No buffer space available
> Jul 28 15:22:27 mako kernel: wlan0: link state changed to DOWN
> Jul 28 15:22:27 mako kernel: lagg0: link state changed to DOWN
> Jul 28 15:22:27 mako wpa_supplicant[329]: wlan0: CTRL-EVENT-DISCONNECTED bssid=c4:04:15:90:f5:fd reason=0
> Jul 28 15:22:27 mako wpa_supplicant[329]: wlan0: CTRL-EVENT-SSID-TEMP-DISABLED id=2 ssid="neural_network" auth_failures=7 duration=90 reason=CONN_FAILED
> Jul 28 15:22:28 mako login: ROOT LOGIN (root) ON ttyv0
> Jul 28 15:22:31 mako dhclient[533]: send_packet: Network is down
> Jul 28 15:23:06 mako last message repeated 4 times

This is my hardware:

> iwn0_at_pci0:3:0:0:        class=0x028000 card=0x13118086 chip=0x00858086 rev=0x34 hdr=0x00
>     vendor     = 'Intel Corporation'
>     device     = 'Centrino Advanced-N 6205 [Taylor Peak]'
>     class      = network


I know I had this working at one point on 10.2-RELEASE, but recently
I've tried both 11.0-BETA2 and 12-CURRENT and get this behavior.  Any
advice for debugging?