The Mystery of Mr Andrew and Dr Andy
This is not a sign of incipient schizophrenia but simply a culture thing. Let me explain. For many years I followed the traditional English scheme where I was "Andrew" to strangers and "Andy" to closer acquaintances. But then I moved to France. French culture is different. People normally use the full first name and you would only use a shorter form in a close family situation, perhaps not even then. This means that pretty much everyone in France calls me Andrew or M Hennigan, even if I asked them to call me Andy. To them it seems too familiar and a bit childish, like using one of the names people use for small babies. At first I found this awkward, but now I am used to it, so when I write to someone in the USA I sign Andy, and when I write to French people I sign Andrew. And, of course, sometimes I get it wrong.
This culture difference can create real problems. Let me tell you the story of a colleague in Europe who worked for an American boss who we will call David. When this European wrote to David he wrote the name in full, but he always replied back signing "Dave". This actually created some tension because to the American boss using David when he has started using Dave is a sign that you are being deliberately cold and trying to push him away. But to many Europeans to insist on using "Dave" sounds very disrespectful.
It is often in small details like this that cultural misunderstandings can make email communication very difficult. Most people actually attach meanings to little things like the way the name is written, the people who are copied and so on. Some people even analyze the "regards" at the end to see if they are "best", "warm" or just plain cold "regards", which they interpret as "I hate you".
One day I will post an article about this on my website, too!