The unknown extra white space is always there, even without a comment. It places the title on the top and the file stats on the bottom; This feature does require a valid doctype tho. Just like alot more: the arrow that points at the comments looks retarded without a valid doctype and the alignment you mentioned yourself.
If you can live with all these errors, then go ahead and remove the doctype.. but im not planning to re-write more than the half of the code to just make it compatible with a floating "TOP" button
Besides, im sure there are other methods for creating the button.