How old is the dog? How old was it when first introduced to live birds? Did it get slapped around by a bird as a pup? Blinking has alway's been a problem with Springer's and I'm not sure why. I haven't worked with them in a lot of years but, some thing's hold true with all breeds. I've seen pointing dog's go soft because of to much handling by their owner's. I've seen them quit picking up bird's at all because of being slapped around by a bird as a pup. I believe these things are a confidence problem created in a young pup by doing to much to soon. If that is the case here, the dog need's it's confidence re-built. Sometime's to fix problem's like that you have to create another that will also have to be fixed.
This dog, is it steady to wing and shot? If so, you might try letting it go. Also if your shooting around the dog, you might quit. I would assume that your seeing this happen at fun or training day's and gun's are present. Try putting down pigeons with flight feathers pulled and running the dog without the gun. The dog might be a bit soft and is antisipating the shot. If the dog start's rushing the bird's and grabbing them, let him. Then go back and re-introduce the gun properly. Don't as many suggest, use a bird with the dog chasing as a distraction for the gun fire. What generally happen's is that an already soft dog associates the gun fire with the bird.
For sure, what ever causes this thing called blinking, I believe it to be man made. Either by improperly introducing the gun, the live bird or over handling. In the case of over handling it could well be the pressure put on a dog to break it to wing and /or shot. I have watched many different methods used to break pointer's and most are,,,not harst but more like tuff love AND involve a bird. A soft dog become's softer to the point where some scent the bird and leave. If that might be the problem, I have a very good method for breaking a dog that put's no pressure on the dog. In the pointer world the "Hup" command sounds like "whoa". Both commands should be taugh away from birds and never used around bird's until the dog is 110% in the training yard. The dog learns most of what it knows thru association; associate nothing even remotely bad or unpleasant with a bird. That even applies to force retrieve training. Done properly, it is NEVER done with a bird, dead or alive. The bird is introduced AFTER the force training is completed.
I don't know if any of this will help you as it's been a long time for me with Springer's. But keep in mind, 99% of the dog's are not born that way, we make them that way, usually by asking to much to soon.
Good luck.
I just went back and re-read your post. He walk's around them but won't flush but does retrieve well. If he put's nothing in the air and catches nothing on the ground, he should have nothing to retrieve. Maybe some one worked on retrieving with dead birds to soon and the dogs believes hes not allowed to pick up live birds? Try taking the dog out with live birds with their wings tied to their body and do a few retrieves. You want the birds to be walking around when the dog goes for them AND make short throw's so he can keep the bird in sight at all time's. The only thing you'll be concerning yourself with is his retrieving, which is not a problem. Have him retrieve live birds, wings tied please, we don't want the dog slapped around by a bird just yet!