`crux-duplicate<-and-comment>-current-line-or-region` using regions blends lines about crux HOT 2 CLOSED

(defun jnf/duplicate-current-line-or-lines-of-region (arg)
  "Duplicate ARG times current line or the lines of the current region."
  (interactive "p")
  (if (use-region-p)
      (progn
        (when (> (point) (mark))
          (exchange-point-and-mark))
        (beginning-of-line)
        (exchange-point-and-mark)
        (end-of-line)
        (goto-char (+ (point) 1))
        (exchange-point-and-mark)
        (let* ((end (mark))
               (beg (point))
               (region
                (buffer-substring-no-properties beg end)))
          (dotimes (_i arg)
            (goto-char end)
            (insert region)
            (setq end (point)))))
    (crux-duplicate-current-line-or-region arg)))