I changed this behavior. When you clear the complete content of the editor box and press "Save draft", the complete row in the drafts table of the database now gets removed and no traces of the draft saved before remain.
I remember there was some reason I prevented saving empty drafts, but I do no more remember why. During my tests I couldn't find issues with the new version, so let me apply the Banana Principle and ripe my product by you clients ;-)