Invisible overlays on the first line of the buffer makes the first key hidden

[MartinRykfors]

Create an elisp buffer with a few lines of text in the beginning.
Enable key-leap.
Execute the following (it inserts an invisible overlay from the beginning of the buffer to a few lines down)

(progn
  (let* ((start (point-min))
         (end (save-excursion
                (goto-char (point-min))
                (forward-line 3)
                (point)))
         (ol (make-overlay start end)))
    (overlay-put ol 'invisible t)))

The topmost key in the margin is now missing.