Been a while since I got back to this one....

I'm with Ben on the stab size. That's just way to small. Sure it'll fly since it's a symetrical airfoil and they don't need much stabilizing force but couple the small size with the high drag and possible pitch coupling from a sudden and large rudder deflection and all kinds of mysterious things can happen. Even just going back to my sudden braking action may be enough that the small stab can't provide the proper lift any more and so the nose drops.