this has been known for a while. I first posted about this I 2012 :
http://forum.mikrotik.com/t/v6-rc6-released/62201/1
also later http://forum.mikrotik.com/t/v6rc14-released/65819/32 and http://forum.mikrotik.com/t/v6-0-released/66371/59
There is also a support ticket : Ticket#2013061066000546
The Vrf, has been unstable in all releases of 6.x