Yes, it is very common. Unfortunately many general practice vets do not have a lot of experience in properly interpreting x-rays, or even taking x-rays with proper positioning (as is evidenced by many threads in the Show Me Hips) section. This often leads to misdiagnosis. I have seen a few cases of regular GP vets saying a dog didn't have a problem when one was clearly there, and many, many, many cases of GP vets saying that there was a huge problem, including recommending euthanasia or surgery to fix it, when in fact there was no problem at all. I even know of one puppy put down at the vet's recommendation because he was showing pain, when in fact the pup had pano and not HD.. as was obvious on the x-ray when they were viewed by a competent ortho specialist at a later time, but unfortunately the puppy was already dead. And another case where a club member was told by his vet, at a very fancy, supposedly well respected clinic, that his OFA Good rating was dysplastic and anything less than Excellent means that the dog had dysplasia. A simple read through the OFA website would contridict that, but this vet was completely convinced that her totally inaccurate, ignorant opinion was correct and shared it with who knows how many clients.
Most breeders seek out vets who are very experienced and qualified with regard to hip and elbow x-rays so more often than not they are working with a vet who is better at this than the vets many customers use. This is why for contracts/warranties getting an impartial, qualified opinion via something like OFA is the way to go.