pfSense

On an Alix 2D13 with WiFi card in it.
2.2-BETA (i386)
built on Sun Nov 16 14:10:12 CST 2014
FreeBSD 10.1-RELEASE

Traffic Graph (from Status menu or the widget) always shows 0 traffic out on the WiFi interface to clients. Traffic in from clients shows correctly.
Root cause seems to be:
$ifinfo = pfSense_get_interface_stats('ath0_wlan0');
var_dump($ifinfo);
array(11) {
["inpkts"]=>
int(926911)
["inbytes"]=>
int(80903838)
["outpkts"]=>
int(1464350)
["outbytes"]=>
int(0)
["inerrs"]=>
int(16)
["outerrs"]=>
int(412)
["collisions"]=>
int(0)
["inmcasts"]=>
int(9751)
["outmcasts"]=>
int(0)
["unsuppproto"]=>
int(0)
["mtu"]=>
int(1500)
}

outbytes is zero.

And outbytes is not appearing in 'ath0' either (just checked that in case it ended up in the wrong place):
$ifinfo = pfSense_get_interface_stats('ath0');
var_dump($ifinfo);
array(11) {
["inpkts"]=>
int(982945)
["inbytes"]=>
int(0)
["outpkts"]=>
int(1127117)
["outbytes"]=>
int(0)
["inerrs"]=>
int(22129)
["outerrs"]=>
int(0)
["collisions"]=>
int(0)
["inmcasts"]=>
int(0)
["outmcasts"]=>
int(0)
["unsuppproto"]=>
int(0)
["mtu"]=>
int(2290)
}

Ordinary interfaces are working fine, e.g vr0,vr1,vr2 and also VLAN devices like vr0_vlan50.