If you look at the rear of the wing mount area, you can see that the distance between the canopy rail and the wing cutout is quite short. This is where they break if they are going to as it is the weak point. The structure from that area back is very lightweight.

Both times mine broke, I was flying in very gusty winds. Both times I landed successfully, and afterwards a gust of wind picked the airplane back up. When it fell down, it broke right in that weak spot both times. There is a really long Twist thread here in the forums, and others have mentioned the same problems. I don't think my fix of adding 1/8" ply doublers in that area added much weight, but it's much stronger.

AV8TOR