That is worrying...
This is worrying on a couple of levels.
1. This means that they consider something worth stealing at least as much as in F35 and friends. Maybe Jane's Defense has a point regarding Russia catching up technically.
2. They have failed to correctly reproduce it from the 3 aircraft they bought on a contract for 130 before canceling the rest of the contract. That is same as 1 actually, just this means that the tech in the 3 they had delivered was significantly higher than their copying acumen. So high they they could not reverse engineer it even with an example in their hands. Again, maybe Jane's Defense has a point.