How Hot is your Transformer?
Most transformers will give off heat. I don't know if 50C is too hot but most transformer components are rate either 75C or 90C. I suppose you could give Hammond Manufacturing a call and ask their engineering department. 
A simple transformer is basically two coils so your primary side is always passing current. Due to that you have a lot of EMF or Magnetic opposition which is the cause of the heat. I won't get more involved in transformer technology since it is about a one semester course and I don't want to bore you or myself to death by trying to explain any more than I have. I will say it does rise in temperature under heavier loads.
An autotransformer will also give off heat. Your particular transformer is shielded and for that reason probably will give off more heat and it is an isolation transformer, and an autotransformer is not. So really not comparable.


Hope this helps