This is just my opinion and may not be worth spit but I think it is the responsibility of the hobbiest (in this case you) to inspect the plane as you assemble it. I recently built the GSP Katana and found a number of problems with it, one of which was a lack of lite ply reinforcing one of the elevator servo mounting points. Notice I said ONE of them, as there are two. I just cut a couple of pieces of ply and glued them in, went on and never gave it a second thought. The incidence was off on one of the Stabilizers as well. I corrected that too. Had to add 15 oz. of weight to the nose to get the plane to balance at the recommended point, using the recommended size engine.

If you just blindly assemble a plane from any manufacturer, you can probably expect it to come back and bite you in the @$$. GSP is taking a real beating on the Katana because of a bad design in the wings and most of the original production run have come to an early demise. On those planes they are making good on the losses (although grudgingly) and in the newest production run they have fixed the problem. It sounds to me like, based on my experience with this and other manufacturers, you just have a plane that a part was mistakenly omitted from. Technically, GSP might share some responsibility, but you as the builder should have noticed and repaired their omission during the assembly process.

You put a dangerous machine in the air you have the responsibility to make sure it is safe as possible. I don't mean to imply that you should tear all your planes apart to make sure they are built like a tank, but something like that you should have noticed, if you were as experienced as you say.

Just my opinion as stated above.