Liz
My GtGt Grandfather had two sons with my GtGt Grandmother, one was called John b1884. My GtGt Grandmother died in 1886 and then by 1891 Census the two boys were living with their Grandparents. My GtGt Grandfather remarried and they also named a son John who was born in 1890. I also have no idea why they did this as the first John was still alive and not even a family name as my GtGt Grandfather was James as was his Father. I have assumed that his second wifes Father may have been John and she may have wanted one of her sons thus named. So, not unheard of but probably not a common occurrence. On a lighter note I do remember seeing one family on a Census with seven daughters named Mary, all with a middle name, so can only assume they were known by their middle names!!
Sandra