... Just my humble observations.
When you shoot a flyer out of order, it generally tends to mess with some dogs. They want that flyer! And quite often they tend to expect to be able to retrieve it first.
In this case, the flyer is shot first and there remain two dead bird marks, a hen pheasant and a duck. Both of these birds are across a piece of water, while the flyer is a run on land. Both dead birds are also retired. The go-bird is the dead bird duck.
Many dogs are disenchanted with this scenario. "You want me to get that dead bird first?" With the guns retired, some dogs don't focus and concentrate on that right bird when sent, and they end up splitting the difference between the right and middle birds en route. Then they must make a decision on which bird they're actually after. When this happens, on this test thus far, most of them tend to wind up back over at the right hand bird, but at least a few have wound up with the middle bird.
Also, some dogs, when sent for the middle bird last, end up hunting with temptation toward the flyer and this has produced some problems in dog work, also. Never mind it's already been retrieved except in the case of a dog confused on his/her first send. Another factor that pushes dogs toward the flyer on the middle bird is a rather large and nearly impenetrable sprawling brier patch basically on line to the middle bird on the far land deep of the pond.
Wind is also a factor depending which way it blows but that tends to go without saying. At times it's been tough to miss either dead bird.
So, these factors have influenced a lot of dogs, in my opinion.