isend: Why additional C-RET required when sending code to ansi-term?

Question

The following code (from here) allows to send lines of code to an open *ansi-term* buffer via C-RET. It works well but the very first time I hit C-RET, the current line is not sent (nothing happens). Only from then on does C-RET send the current line to the *ansi-term* buffer. Why is the additional C-RET required in the beginning?

(defun isend-with-ansi-term ()
  (interactive)
  (let ((term-buf (get-buffer "*ansi-term*")))
    (unless term-buf
      (display-buffer
       (save-window-excursion
         (save-current-buffer
           (setq term-buf (ansi-term (or explicit-shell-file-name
                     (getenv "ESHELL")
                     shell-file-name)))))))
    (isend-associate (buffer-name term-buf))))
(define-key global-map [C-return] 'isend-with-ansi-term)