I can hammerhead my Kadet, but the 4* noses over when I try it.  Really confuses me too.  It also likes to yaw left on the vertical, so I need right rudder for it to go straight.   It doesn't have enough vertical either. If I try to do a 4 point roll on the vertical, I get 2 points and it falls over.   This is one of the reasons I'm considering a Bridi.