I might just be being a little PFB, but yesterday I took my DD to be weighed at the midwives drop in centre. The lady who was registering us took my name, then DD's. She started writing the same surname as mine and when I told her it wasn't she looked appalled and asked why DD had a different surname. I told her it was her fathers and she still looked utterly baffled, so I explained we aren't married yet. There was very little small talk after that!
I'm obviously not hideously offended or anything, but surely there aren't that many reasons a child would have a different surname to the mother and really, why question it? Just seemed a bit off.