I once met a woman in the US who grew up in the UK and had indefinite leave (like the rest of her family) and then went home to the US to study. When she came to the UK for a visit, a prat IO cancelled her ILR.
She probably should have applied for citizenship by registration too, on the basis of having lived here so long. Per what Garry recently posted, the Home Office apparently has a huge amount of discretion to grant British citizenship to people who have lived here during childhood.