If the area is empty to start with then the appropriate tags appear to be entered by default (if you've chosen divs then these appear, p tags then you get an opening and closing p tag, etc.
If the area has something in it when it opens (a basic bit of text) then this is fine and you can edit to your hearts content.
As I say, not sure why if the field is empty that it inserts either div, p or br tags before you edit the field.