Zanussi Fridge/Freezer ZX 57/3W. Freezer sealing or defrosting problem? ?

Having replaced the entire door on a Zanussi freezer with a brand new one because of a broken and leaky seal I find that ice is still building up inside the freezer under the food trays and around the upper edges of the door. This eventually leaks out to puddle onto the floor.

The new door appears to seal well, is there a self defrosting problem and how may I resolve it?