I have seen that before. It is the design of the rocker system in combination with spring pressure. The head is not strong enough for how the valvetrain bolts on. High spring pressure and big ports will eventually cause this. They really need a better way of anchoring the rockers.
2015 Pro Stick Champion
2007 NSCA Champion
422 All Stars runner up 2008, 2009, 2010
95' G Force NA10.5 Mustang firstname.lastname@example.org
04' G Force Mustang email@example.com
64' Dyno Don Comet Wagon firstname.lastname@example.org