I don’t believe the majority of the time it’s the birds doing I think the majority of the time the human messed up somewhere along the lines and just didn’t noticed or won’t admit it even if they did.
That being said I’ve had my fair share of screwy ones along the way, but one can’t blame awhole line or the ones ya got them from 100% either. Once they are yours they are yours.... you breed em you cull em along the way for the the things you dislike. With new crosses you get a wider variety especially if it’s a new cross with birds from totally different people. Everyone has an idea of what they are after it may not be your idea and may not suit you one bit.
What’s here that I’ll breed is because I like them and they suit me from up north, down south and across the ocean. I’m happy with em.