This is burocracy at work, silly as it sounds. Had the same happen to me when I applied for a new passport I was actually forced to prove my citizenship down to the birth certificates of my parents. Mind you I travel for business and I'm probably on my sixth passport and it was the same people were I had received my previous one.

When they told me I just looked at them and asked them if they were kidding. Being Germans they had no sense of humour and I organised the documents which isn't easy if you need originals that are 70 years old.

Sounds like a bad joke but the gentleman in front of me had the same problem and he was probably around 70 years old and they asked him that he must provide the birth certificates of his parents. He simply said this is absolutely not possible because they don't exist. So all your life you travel with a passport and then they tell you that you are probably not a citizen because some documents can't be provided.