vnStat not auto adding new interface

[pwnell]

I added a new VLAN based interface to my pfSense 2.5.1 but vnStat did not pick up on the new interface. Restarting vnStat made no difference. Only way I could fix it was to run on the console:

/usr/local/bin/vnstat --add -i ix0.88
/usr/local/bin/vnstat --setalias SECURITY -i ix0.88

Is this a bug or expected behaviour?